Two SIP trunk quotes can look almost identical and still cost very different amounts a year later. The difference usually isn’t in the headline channel price. It’s in the lines most people skim: call charges, number fees, setup costs and contract terms.
The timing makes this worth doing properly. The UK’s legacy phone network is due to be retired on 31 January 2027, and Openreach has said it will not be delayed again. Many businesses are comparing quotes for the first time in years, and unfamiliar jargon makes it easy to compare the wrong things.
This guide walks through a typical quote from top to bottom.
Before You Compare: Give Everyone the Same Brief
Quotes only line up if they’re based on the same assumptions. Before you ask for any, write down:
- How many simultaneous calls you need (your channel count)
- Which numbers you want to keep or add
- Your typical monthly calls to UK landlines, mobiles, 03/08 numbers and abroad
- Your PBX make, model and software, or whether you need a gateway
- Whether you need call recording, failover or multiple sites
Send the same brief to every provider. A quote built on a guess about your call volumes can’t be compared with one built on real data.
The Quote, Line by Line
Channel Rental
This is the monthly fee per channel, meaning per simultaneous call. It’s the number most providers lead with, and it’s the least informative on its own.
Check whether it covers only the channel or includes anything else, such as a set of numbers or a call bundle. Check also whether the price changes with volume. Some providers tier it, so the tenth channel costs less than the second.
Number Charges (DDIs)
A DDI, or direct dial-in number, routes calls to a particular person or department. Some quotes include a block of numbers, while others charge per number each month. If you hold dozens of old numbers, this line can outweigh the channel rental.
Ask whether you’re paying for numbers you no longer use. A migration is a good moment to tidy them up.
Number Porting
Porting moves your existing numbers across. Look for a one-off fee, a per-number fee or both, and ask about timescales. Check that old lines stay live until the move is confirmed, and ask what happens to numbers if you later leave.
Call Charges
This is where quotes diverge most. Look for separate rates for:
- UK landlines (01/02 numbers)
- UK mobiles
- Non-geographic numbers such as 03, 08 and 09
- International destinations, listed by country
- Premium-rate numbers, which are often blocked by default
Look for connection fees on each call and the billing increment. Per-second billing and per-minute billing can give very different totals on short calls. Make sure the rates are the ones you’ll actually pay, not the cheapest rate in a long list.
Bundles and “Unlimited” Calls
Many quotes include a bundle of minutes or an “unlimited” allowance. Read what’s behind it:
- Which destinations are included, and which are excluded
- Whether there’s a fair-use cap and what it is
- Whether unused minutes roll over
- What the overage rate is once you exceed the bundle
An allowance that covers UK landlines but not mobiles may be worth little to a sales team that mostly calls mobiles. Compare the bundle against your real call mix.
Setup and Installation Fees
Check for one-off charges covering provisioning, configuration, testing and engineer time. Some providers waive these on longer contracts, so ask whether the fee is truly gone or just moved into a higher monthly price.
Hardware: Gateways and SBCs
If your PBX can’t speak SIP directly, you may need a gateway. A quote might include it as a purchase, a rental or a managed service. Ask who supports it, what happens if it fails and whether there’s a replacement guarantee. For some setups, a Session Border Controller is also needed to protect and manage traffic.
Connectivity
SIP trunks depend on your internet connection. Some quotes bundle connectivity, such as business fibre or a leased line, while others assume you already have it. Make sure you know which, and whether the connection is suitable for your channel count and any failover plan.
Resilience and Failover
Look for what’s included: automatic diversion to mobile numbers, backup routes, a second connection or geographic redundancy. If it isn’t listed, assume it isn’t included, and ask what it would cost.
Extras
Call recording, reporting, number presentation features and Microsoft Teams integration are sometimes included and sometimes priced separately. Add these to your comparison if you need them.
Contract and Commercial Terms
This section of a quote is easy to skip. It shouldn’t be.
Minimum term. How long are you committed, and what happens at the end? Some contracts roll over automatically.
Early termination. What does it cost to leave early? Is it a fixed fee, or the remainder of the term?
Price reviews. Can the provider raise prices during the contract, and with how much notice? Can you leave if they do?
Changing channels. Can you add channels quickly? Can you reduce them without penalty?
Service levels. Look for an uptime commitment, response times for faults and what remedy applies if they’re missed, such as service credits.
Support. Check hours, location and how you contact them. Support may be included or charged separately.
VAT. Business quotes often show prices excluding VAT. Make sure you compare like with like.
How to Compare Quotes Side by Side
Once the quotes arrive, work through them in the same order, one provider at a time. For each, write down the channels quoted, the monthly channel rental, any number and porting charges, the rates for UK landlines, mobiles, 03/08 numbers and your most-called countries, what the bundle includes and excludes, how calls are billed, setup and hardware costs, whether connectivity and failover are included, the minimum term, the cost of leaving early and the support hours.
Keep the notes in the same order for every provider, so gaps stand out. If one quote leaves a line blank, that’s a question to ask, not a zero.
Then work out an estimated annual cost for each, using your real monthly call mix. That single figure is far more useful than any individual line.
Reading Between the Lines
You’ll find plenty of lists of the best UK VoIP providers online, and plenty of searches for the cheapest UK VoIP providers. Neither tells you what a particular SIP trunking service will cost your business once calls, numbers and extras are counted.
Treat unusually low channel rentals with curiosity, not excitement. Ask where the money is made. It might be mobile call rates, setup fees, a long minimum term or support charged separately. A quote can be cheap on one line and expensive overall.
Red Flags
- A channel price with no call rates
- “Unlimited” with no written definition of fair use
- Setup, porting or gateway costs missing entirely
- Vague answers about failover or support hours
- A long minimum term pushed before you’ve seen the migration plan
- No written service levels
- Pressure to sign quickly
None of these is automatically a deal-breaker, but each deserves a direct question.
A Realistic Example
A 25-person estate agency receives two quotes for business SIP trunking. Provider A advertises a low channel rental but charges noticeably more for calls to mobiles and has a three-year minimum term. Provider B charges more per channel, includes a mobile-heavy bundle, offers a shorter term and includes automatic diversion to mobiles.
On the surface, A looks cheaper. Once the agency applies its real call mix, most of which goes to mobiles, B comes out lower over a year, and offers better resilience. Without the line-by-line comparison, they would have chosen A.
Questions to Ask Every Provider
- Can you show a worked example based on our actual call volumes?
- What’s not included in this quote?
- How are calls billed, per second or per minute, and is there a connection fee?
- What does “unlimited” exclude, and is there a fair-use cap?
- Can prices change during the term?
- What does it cost to add or remove channels?
- What happens to our numbers if we leave?
Wavetel Business is one example of a UK provider you might speak to when comparing quotes, and any provider offering a SIP trunking service should be willing to put pricing, inclusions and terms in writing.
Frequently Asked Questions
What should a SIP trunk quote include?
Channel rental, number charges, porting fees, call rates by destination type, setup costs, any hardware, connectivity, contract terms and service levels. If a line is missing, ask.
Is “unlimited calls” really unlimited?
Not always. Many bundles exclude certain destinations or have fair-use caps. Ask for the definition in writing.
How do I compare quotes from different SIP providers?
Give each the same brief, note the same lines for every quote in the same order, and calculate an estimated annual cost using your real call mix.
Why are some SIP trunks so much cheaper than others?
It may be efficiency, but it can also reflect higher call rates, extra charges, longer contracts or less support. Look at total cost and terms, not just channel rental.
Can I negotiate a SIP trunk quote?
Often, yes. Setup fees, contract length and bundle contents are common areas for movement, particularly if you commit to a longer term or larger volumes.
Conclusion
Reading a SIP trunk quote properly means looking past the headline channel price. The real cost sits in call rates, numbers, setup fees, hardware and contract terms, and resilience and support matter as much as price.
The practical takeaway is to write one clear brief, send it to every provider and note the same lines from each answer, in the same order. Calculate an estimated annual cost from your real call mix, then ask about anything that’s missing. Start well before January 2027, so you have time to compare calmly.