Open ten provider websites and you’ll find roughly the same promises: reliable, scalable, carrier-grade, great support, no hidden costs. Every one of them sounds like the best choice, which makes none of them easy to choose.
The pressure to decide is real. 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. Businesses replacing ISDN lines are getting calls from salespeople who know a deadline is helping them.
This guide is about keeping control of the process: what common claims actually mean, what evidence to ask for and how to compare offers on equal terms.
Start With Your Own Brief, Not Their Brochure
The most effective protection against a sales pitch is a requirements list written before you speak to anyone. Without one, the provider’s priorities become yours by default.
Write down:
- Peak simultaneous calls, taken from real call logs
- The numbers you hold and want to keep
- Your PBX make, model and software, or your plan to replace it
- What happens to your business if phones stop for an hour
- Your monthly call mix: UK landlines, mobiles, non-geographic and international
- Anything else attached to your phone lines, such as alarms, fax, lift lines and card machines
- Whether you need call recording, multi-site routing or Microsoft Teams
Send the same brief to every provider and judge them on how well they answer it. A provider who ignores half of it and steers back to their standard package is telling you something.
Decoding Common Claims
“Carrier-Grade”
This phrase has no fixed meaning. It’s meant to suggest telecom-quality reliability, but any provider can use it. Ask what it means in practice: how many data centres, how many upstream carriers, what happens when one fails and who monitors the platform out of hours.
“99.999% Uptime”
Percentages sound precise, so do the arithmetic. Five nines allows about five minutes of downtime a year. Even 99.9%, which sounds excellent, allows nearly nine hours. The questions that matter are:
- What exactly is measured: the platform, the network or your whole service?
- Are planned maintenance windows excluded?
- What do you receive if the target is missed?
- Is it a commitment in the contract or a marketing aim?
A target with no remedy is a hope, not a guarantee.
“Unlimited Calls”
Look for the definition. Unlimited usually means certain destinations, within fair-use limits. Mobile calls, non-geographic numbers and international calls are often excluded or capped. Ask for the list of exclusions in writing.
“No Hidden Fees”
Ask for a complete list of every charge you might see in the first year, including setup, porting, gateways, extra channels, call recording, support and early termination. Then ask: “Is there anything not on that list?” Their response tells you how comfortable they are.
“Free Setup”
Free setup sometimes means the cost sits in a longer contract or a higher monthly price. Ask what the total cost would be with and without the free setup, and what term it depends on.
“Works With Any PBX”
Ask for evidence: have they connected your make, model and software version before? Can they share a configuration guide or a reference customer? “Any PBX” is a sales line. A tested integration is a fact.
“24/7 Support”
Find out what that means. Is it a person who can fix the fault at 2am, or an answering service that logs a ticket for the morning? Ask who owns the problem when it’s unclear whether the fault is in your network, your PBX or their platform.
“Best SIP Provider in the UK”
You’ll see this on provider sites and on comparison pages alike. Treat both with care. Many comparison pages earn money from the providers they list, and none of them knows your PBX, sites or call mix. A provider that’s best for a large contact centre may be a poor fit for a ten-person firm.
Evidence Worth Asking For
Claims are cheap. Evidence is harder to produce, which is why it’s useful.
Reference customers. Ask to speak to two or three customers of a similar size and sector, preferably ones who’ve been through a migration. Ask what went wrong, not just what went well.
A sample contract and service levels. Read the real terms, not the summary page. Look at minimum terms, exit costs, price-change rights and what the SLA actually promises.
A working bill. Ask for an example invoice based on your real call mix, including forwarded calls and non-geographic numbers.
A migration plan in writing. Who does what, in which order, with which dates, and what happens if porting slips?
A test trunk. A short trial with a few channels and a spare number shows how the service behaves with your PBX and your network. It tells you more than any demo.
Network and status information. Ask whether they publish incident history and how they communicate faults.
If a provider won’t provide these, note it, and weigh it.
Spotting Pressure Tactics
Some pressure is natural, since sales teams have targets. Be wary when it replaces answers.
- “This price is only available today.” Real prices rarely change overnight. Ask for the offer in writing with an expiry date.
- “Capacity is running out before the deadline.” Engineering and porting capacity can tighten as deadlines approach, so there’s some truth to this, but it’s no reason to skip due diligence.
- A long minimum term is pushed before the plan is clear. Term length should follow trust, not precede it.
- Reluctance to discuss exit. A provider confident in its service will explain how you’d leave.
- Vague answers to specific questions. “We’ll sort that out during onboarding” isn’t an answer to “who is responsible for failover?”
A Fair Way to Score Providers
Once you have written answers, score each provider on the same few areas, weighting them for your business. Keep it simple: a score from one to five for each, with a note explaining why.
The areas that usually matter most are:
- Resilience and failover, and how they handle outages
- Support quality, hours and ownership of faults
- Fit with your PBX and setup, backed by evidence
- Total cost over the term, calculated from your real call mix
- Contract terms, including exit, price changes and flexibility
- Migration help, including porting experience and testing
A business where downtime is costly might count resilience double. A small team on a tight budget might cost more, but should still treat resilience, support and fit as a minimum, not an extra.
Have two people score independently before comparing notes. It reduces the influence of a charming salesperson.
Cheap Doesn’t Mean Bad, and Expensive Doesn’t Mean Good
You’ll see lists of the cheapest UK VoIP providers and the best UK VoIP providers, and you may be tempted to start from either. A low price can reflect efficiency, or it can come from expensive call rates, long terms or thin support. A high price can reflect real resilience and service, or just a bigger sales team.
Neither price nor ranking tells you whether a SIP trunk service fits your business. Ask each provider to explain, plainly, why their price is what it is.
A Realistic Example
A 28-person property management firm in Leeds is replacing an ISDN30 line. Three providers have impressed them with confident pitches. All three claim reliable service, strong support and fair pricing.
The firm writes a one-page brief and sends it to each. One provider replies with its standard package and doesn’t mention the firm’s fax line or alarm. Another gives detailed answers and a worked bill but pushes a three-year term. The third gives similar answers, offers a test trunk and agrees to a shorter initial term. Reference calls reveal that the second provider’s support is slow at weekends, while the third has handled two similar PBX migrations.
Scored independently, the third comes out ahead. It wasn’t the cheapest, and it wasn’t the loudest. It was the one that answered the brief with evidence.
A Short Checklist
- Write your brief before speaking to providers
- Send the same questions to every provider
- Ask what each marketing claim means in practice
- Request references, sample contracts, a worked bill and a migration plan
- Test a trunk before committing
- Score each provider independently against the same criteria
- Don’t sign under artificial deadline pressure
Wavetel Business is one example of a UK provider you might speak to, and any provider offering a SIP trunk for business should be willing to answer these questions in writing and back claims with evidence.
Frequently Asked Questions
How do I compare SIP trunk providers fairly?
Write one brief, send it to every provider, ask for written answers and evidence, then score each on the same criteria. Calculate total cost from your real call mix.
Is “carrier-grade” a meaningful claim?
Not by itself. Ask what it means: how many data centres and carriers, how failures are handled and who monitors the service.
What should I look for in an uptime promise?
What’s measured, whether maintenance is excluded and what remedy applies if the target is missed. A percentage without a remedy is a marketing aim.
Should I trust comparison websites?
Use them as a starting point. Many are paid by the providers they list, and they can’t account for your PBX, sites or call volumes.
Can I trial a SIP trunk before committing?
Often, yes. Ask for a test trunk with a few channels and a spare number, and check how it behaves with your PBX and network before porting anything.
Conclusion
Comparing SIP trunk providers without being swayed by the sales pitch comes down to having your own brief, asking what claims actually mean and insisting on evidence. The best signals are specific answers, written terms, reference customers and a willingness to let you test.
The practical takeaway is to write your requirements this week, send the same questions to every provider and score the answers independently. Start well before January 2027, so you can compare calmly instead of deciding under pressure.
