Most articles frame this fight wrong. They ask which technology is cheaper. That is not the question.
The real question is simpler. How many calls does your business have going at the same time? Most offices on a PRI are paying for 23 channels and peaking at 6 to 10. Once you know your true number, the answer mostly picks itself. Usually it is SIP. Not always. The exceptions are real, and we will name them.
Stop comparing technologies. Count your concurrent calls.
Peak simultaneous calls is the only input that matters. Everything else is noise until you have it.
You can get it three ways. Pull the trunk utilization report from your PBX. Pull your carrier call records for a busy month. Or run Erlang B against a 1 percent blocking target if you only have total minutes. A 40-person office rarely peaks above 8 to 10 calls at once. If you are paying for 23 channels, you are paying for air.
What a PRI really costs, line by line.
A PRI quote looks clean. The bill does not.
You get a monthly rate, usually $450 to $900 depending on your market and your local phone company. Then the access charge for the loop. Then local minutes, which range from unlimited to a fixed block. Long distance runs $0.02 to $0.05 a minute. The Federal Universal Service Fund adds roughly 30 percent on top of the interstate portion. State and local telecom taxes pile on after that. And the PBX needs a PRI card, a one-time cost of $800 to $2,500.
Add it up. A real 23-channel PRI lands around $700 to $1,100 a month, all in.
What SIP really costs, in both pricing models.
SIP is not one price. It is two, and picking the wrong one can cost more than the PRI did.
Per-channel pricing runs $15 to $30 per call path per month. Metered runs about $0.008 to $0.02 a minute plus a small platform fee. Then the fees that always show up. DIDs at $0.50 to $2 each. E911 at $1 to $3 per DID or per location. A regulatory recovery fee. And a minimum monthly commitment buried in the contract.
The non-carrier costs are real too. Each call on G.711 needs 85 to 100 kbps. So 10 calls needs about 1 Mbps of guaranteed upstream. You need a router that can do QoS, or a separate voice circuit. And if your PBX is not SIP-native, an SBC or gateway runs $500 to $3,000 one time.
Three worked break-evens.
A professional office peaking at 6 calls. Per-channel SIP at 6 paths plus headroom beats the PRI by $400 to $600 a month. Easy call.
A firm peaking at 15 calls with heavy outbound minutes. Per-channel SIP still wins. Metered might not, because the minutes stack up fast.
A 40-call operation running two PRIs, 46 channels, inbound-heavy. Now compare 46 PRI channels against 40 SIP channels. Here a PRI with unlimited local minutes can still hold up. Metered SIP loses to a PRI above roughly 2,500 to 3,000 minutes per channel per month. Know your minutes before you quote.
The costs that aren't on either quote.
PRI is not a stable price. Legacy copper circuits get repriced upward 10 to 25 percent a year once you are out of contract. Carriers are winding this stuff down. The FCC relaxed the copper retirement rules in 2019, so a carrier can exit with 180 days' notice. Terms are usually 36 months with automatic renewal. Early termination fees often equal 100 percent of the remaining monthly charges.
SIP has traps too. The toll fraud clause means you pay if someone steals your credentials, unless the contract says otherwise. Read the metered overage and true-up language. And if voice rides the same internet circuit as everything else, plan for failover.
Run the comparison on your own bill in one afternoon.
Pull the last three months of invoices. Separate the fixed monthly charge from usage. Pull trunk utilization or call records and find your peak concurrent calls. Total your monthly minutes by local, long distance, and inbound. Price per-channel SIP at peak plus 20 percent headroom. Price metered SIP against your actual minutes. Add DID count, E911, SBC, and bandwidth. Then find your PRI contract's end date and the renewal notice window, usually 30 to 90 days before it expires.
The call to make, and when.
If your peak is under 12 and your PRI renews within 90 days, send the non-renewal notice in writing now. Then request SIP quotes at peak plus 20 percent channels.
If your peak is near 23 with high minutes, get your phone company to put the renewal rate in writing. Compare it against per-channel SIP, not metered.
And in every case, ask the PRI carrier one blunt question. Is this circuit on a discontinuance list? Make them answer.