Capacity and calling
Call paths, usage, and numbers sized to actual demand.
Business voice connectivity
Compare SIP trunking providers without rebuilding what already works.
Keep your PBX, SBC, and numbers while comparing providers on capacity, compatibility, cutover, resilience, support, and total cost.
Actual SIP trunking pricing comes from the provider proposal for your capacity, usage, numbers, technical requirements, and contract terms. A channel rate or per-minute rate is only part of the bill. Compare recurring charges and one-time work for the same requirement. See the pricing comparison and quote-comparison worksheet.
What a useful SIP comparison includes
Porting and resilience
PBX compatibility, number porting, and outage behavior.
Commercial clarity
Support ownership, contract terms, and quote assumptions.
When SIP trunking is the right product
SIP trunking connects an existing PBX or calling platform to the public phone network over IP, replacing copper lines or a legacy PRI. RFC 3261 defines the signaling that sets up, modifies, and ends calls; trunking connects them to the PSTN. Keeping the platform can make sense when its call flows, contact center scripts, CRM integrations, recording, or hardware still serve you.
If the PBX itself is the problem, such as limited administration, remote access, or vendor support, a new trunk will not solve it. Compare a cloud phone system instead.
Replacing PRI: what needs checking first?
Start with actual concurrent calls, existing contracts, numbers, and devices that depend on the current service. Keeping the PBX requires a supported SIP design; a working PRI connection alone does not establish compatibility.
Check call paths, PBX/SBC requirements, porting, emergency calling, failover, and the circuit underneath.
For the stay-versus-switch worksheet and migration inventory, read SIP trunking vs. PRI: compare costs before you switch.
Which type of SIP trunking provider fits your environment?
Start with the calling system you will keep and who manages each handoff.
Standalone SIP trunks
For a PBX or contact center platform that mainly needs PSTN connectivity. Carrier and wholesale offers differ in purchasing access and support ownership, so identify who manages the trunk, SBC, numbers, and routing.
SIP alongside a broader voice suite
A broader voice provider may fit a phased move from PBX to cloud users. Confirm it supports your current system, how numbers move between environments, and whether the trunk requires other licenses.
Microsoft Teams Direct Routing
For Teams Phone, compare the complete route through a Microsoft-certified SBC and compatible SIP trunk. Identify who runs the SBC, supplies PSTN connectivity, and troubleshoots each boundary.
Your PBX or SBC may narrow the options; SourceNet can help check interoperability and support ownership first.
How does SIP trunking pricing work?
Providers can charge for capacity, calling, and numbers separately or bundle some of them. Per-channel and per-minute charges can appear on the same quote. Compare the complete bill for your traffic, not the lowest advertised unit rate.
| Pricing component | What you buy | What to check |
|---|---|---|
| Channel or call-path charge | Simultaneous calling capacity | Inbound/outbound limits; whether minutes are included |
| Metered calling | Minutes by direction and destination | Rate schedule, billing increments, minimums, and toll-free traffic |
| Bundled calling | Defined usage within a fixed charge | Included destinations, exclusions, acceptable-use limits, and overages |
| Numbers and optional services | Local/toll-free numbers and selected features | Number rental, emergency calling, recording, support, and redundancy |
Which charges recur, and which are one-time?
Recurring costs may include capacity, usage, numbers, emergency calling, managed equipment, and support. One-time costs may include porting, equipment purchases, licensing, configuration, and cutover work. Equipment or licensing can instead be recurring; ask how each quote treats it. Include any old-provider exit or overlap costs separately.
What determines the actual SIP trunking cost?
Use a provider proposal based on your peak concurrent calls, inbound and outbound usage, destinations, number inventory, PBX/SBC requirements, support needs, and contract term. Ask the provider to identify included services, separate charges, exclusions, and any assumptions still awaiting technical confirmation.
Different proposals may cover different amounts of work. Resolve those differences before comparing totals; a published unit rate does not establish the cost of the deployment you need.
Call paths matter more than seat count
Sizing SIP trunks by headcount, one path per employee, is usually wrong in both directions. Most offices rarely have more than a fraction of staff on calls at once, so headcount-sized paths sit idle. Contact centers, dispatch, and other high-call-volume teams have the opposite problem: concurrency can spike well past seat count during peak hours or outbound campaigns.
What matters is your real concurrent call volume at peak, which comes from your call patterns rather than a rule of thumb. Pin it down before comparing quotes.
PBX, SBC, and interoperability
Not every PBX handles SIP the same way, which is where an SBC often earns its place: protocol interoperability, NAT traversal, and the security boundary between your network and the provider's. Some environments need a dedicated SBC; others work with a PBX that has solid native SIP support and a well-configured firewall. The right topology depends on the PBX, the provider, and how much of that boundary you want managed.
Ask about transcoding early too: if your PBX and the provider's network don't agree on codecs, something in the path has to convert between them, which affects call quality and where the processing load sits.
SBC decision factors
- Protocol interoperability, NAT traversal, security
- Native SIP + firewall may suffice
- Topology depends on PBX and provider
- Transcoding needed if codecs mismatch
Codecs and the network underneath the trunks
Agree who validates voice quality, monitors performance, and owns troubleshooting across the PBX, SBC, circuit, and provider before choosing a proposal.
Supporting technical details
That tradeoff depends on call volume and the circuit, and the network underneath matters just as much. Voice doesn't tolerate latency, jitter, or packet loss the way a file download does: Cisco's QoS for VoIP guidance points to the ITU's recommendation of under roughly 150ms one-way latency, jitter buffers that stop helping past about 100ms of variation, and (for a compressed codec like G.729) packet loss held far below 1% to avoid audible dropouts. Congestion on a shared circuit shows up as call quality problems first, which is why QoS (prioritizing voice traffic) is the usual answer; how it's configured depends on your network.
SIP trunking and Microsoft Teams Direct Routing
Direct Routing is the Teams Phone architecture that uses your SIP trunks. A Microsoft-certified SBC, chosen from Microsoft's certified SBC list and configured to Microsoft's Direct Routing planning guidance, sits at the supported boundary between Teams Phone and the carrier's PSTN environment. Teams already reaches the SBC over SIP secured with TLS; it's the SBC, not Teams itself, that peers with the carrier's SIP trunk. That makes the SIP-specific questions trunk compatibility with the SBC, how existing numbers move onto the trunk, and who owns troubleshooting at the SBC and carrier handoff. For Direct Routing versus Operator Connect, Calling Plans, or a separate cloud phone system, see the Microsoft Teams calling comparison.
Porting numbers without making cutover day painful
Porting often goes sideways because of paperwork and sequencing rather than technical setup. Start with a clean DID inventory and the losing carrier's account details; a port request that doesn't match their records is the fastest way to a rejection. Depending on the carriers, you may need a letter of authorization (LOA), a formal port request, and a confirmed firm order commitment (FOC) date before cutover can be scheduled, and each step varies by carrier.
Test inbound and outbound calling on the new trunk before the port completes, not after. Don't cancel service with the losing carrier when the port request goes in; numbers can fail to port cleanly, and you want a fallback (the FCC's number portability guidance flags this exact mistake). Sequencing it as test, cut, confirm, then cancel keeps porting from becoming the reason a migration slips.
E911 is part of the architecture
Emergency calling has to be designed in from the start. A SIP trunk carries voice, not a street address, so dispatchable location has to be associated with each call deliberately, and providers implement that differently; some, like Telnyx's dynamic E911 implementation, resolve location per call. A single-site office is simpler than a multi-site company or remote and hybrid users on one trunk; each needs its own answer for how a 911 call reaches the right address.
U.S. multi-line telephone systems fall under federal requirements (Kari's Law and RAY BAUM'S Act) that generally call for direct 911 dialing without a prefix, on-site notification when a 911 call is made, and dispatchable location sent to the call center. The FCC's MLTS 911 requirements guidance lays out the specifics; this isn't legal advice. Before cutover, confirm emergency calling for every site and class of user through a provider-coordinated testing procedure. Do not place uncoordinated test calls to 911.
What happens when something fails?
Buyers often ask this last, though it matters as much as anything in a quote: what happens to our calls when something breaks? The circuit, PBX, SBC, or provider network can each fail in different ways, so "we have failover" isn't a complete answer until you know which failures it covers.
Inbound and outbound calling can fail independently. Inbound calls might shift to a forwarding number or a secondary site while outbound calling is still down, or the reverse, depending on how the provider and your PBX are configured. If continuity matters, ask how failover works for each failure point, whether it needs a secondary circuit or endpoint, and who triggers it versus who notices it. Answers vary by provider and setup; we help sort that out before you commit.
The circuit your trunks ride on
SIP trunking is only as good as the connection carrying it. When the design calls for it, we can source SIP connectivity alongside business internet, dedicated internet access, or managed SD-WAN, so voice isn't fighting everything else on the same pipe.
Compare the itemized SIP trunking cost
Use the same peak call paths, numbers, destinations, minutes, term, PBX/SBC handoff, emergency locations, porting scope, failover, and support responsibilities for both quotes. Enter zero only when an item is confirmed unnecessary or included; otherwise mark it unquoted.
Match the circuit and QoS assumptions, with a named owner for network testing. Compare monitoring, support hours, and escalation boundaries explicitly; a lower-cost proposal may include less operational support.
| Cost item | Quote A | Quote B |
|---|---|---|
| Monthly capacity or platform | ___ | ___ |
| Monthly usage, including overages | ___ | ___ |
| Monthly numbers and emergency calling | ___ | ___ |
| Monthly equipment, support, and redundancy | ___ | ___ |
| Monthly applicable taxes and fees | ___ | ___ |
| Total monthly cost: M | ___ | ___ |
| One-time porting, hardware, licensing, and implementation: U | ___ | ___ |
| Old-service exit and overlap costs: X | ___ | ___ |
| Comparison period in months: N | ___ | ___ |
| Period total: (M × N) + U + X | ___ | ___ |
If rates or usage vary, total each month's cost instead. Do not count bundled items twice.
Technical references
The specs and documentation behind this page.
Cisco docs
T1 PRI channel configuration
Reference for conventional PRI bearer and signaling channels.
Read the PRI reference →IETF standard
RFC 3261, SIP: Session Initiation Protocol
How SIP sets up, modifies, and ends a call.
Read RFC 3261 →Microsoft docs
Direct Routing planning guidance
Microsoft's SBC and connectivity requirements for Direct Routing.
Read the planning guide →Microsoft docs
Certified SBCs for Direct Routing
The SBC models and firmware Microsoft supports for Direct Routing.
See certified SBCs →Cisco docs
QoS for Voice over IP
Where common latency, jitter, and packet-loss targets for voice come from.
Read Cisco's QoS guidance →FCC guidance
MLTS 911 requirements
The federal direct-dial, notification, and dispatchable-location rules for multi-line phone systems.
Read the FCC guidance →FCC guidance
Number portability guidance
The rules behind porting, including why not to cancel old service early.
Read the FCC guidance →Telnyx docs
Dynamic E911 implementation
One provider's approach to resolving location per call.
Read Telnyx's docs →Related paths
SIP trunking FAQ
How much does SIP trunking cost?
Actual SIP trunking cost depends on the provider proposal, capacity, usage, numbers, technical requirements, and contract terms. Compare recurring service and support charges with one-time implementation and transition costs for the same scope. Use the worksheet to identify missing charges before comparing available provider options.
How many SIP channels or call paths do we need?
Size for peak simultaneous calls, including any separate inbound and outbound limits. Use call records or a realistic traffic estimate rather than seat count.
Can we keep our existing PBX?
Often, if it interoperates with the proposed service and still meets your needs. Confirm software version, SIP features, codecs, security, and handoff testing.
Can we replace PRI without replacing our PBX?
Possibly, if the PBX can support SIP trunking directly or through an appropriate interoperability design such as an SBC. Confirm PBX capability, licensing, software or firmware, SBC needs, and provider compatibility before choosing the SIP service.
Can PRI and SIP run in parallel during migration?
Some environments can keep the PRI in service while SIP is configured and tested, so calling, routing, numbers, and dependent systems can be checked before disconnecting it. Whether that is possible depends on the PBX, the providers, and the migration design.
Do we need an SBC for SIP trunking?
It depends on the PBX, provider handoff, and security design. Some PBXs support SIP natively; Teams Direct Routing requires a certified SBC.
Can SIP trunking work with Microsoft Teams?
Yes, through Direct Routing with a Microsoft-certified SBC and compatible PSTN connectivity. Operator Connect and Microsoft Calling Plans are other Teams calling architectures that don't use your own SIP trunk this way; compare the Teams options.
How long does number porting take?
It varies by carrier, number inventory, and account records. Get the porting steps and confirmed cutover date before changing the old service, then test calls.
What should we compare between SIP trunking providers?
Use the same capacity, numbers, usage, PBX and SBC details, E911 locations, porting scope, failover, support, and contract term. Compare itemized totals.
Compare SIP quotes for the same requirement
Bring what you know about your PBX, numbers, peak calls, usage, and renewal date. Discuss the requirement with SourceNet and evaluate available provider options. You choose whether to proceed; the selected provider confirms pricing, technical fit, and contract terms.