A finance director in Clerkenwell rings us most Januarys with the same problem. The old on-premises phone system is being switched off, the maintenance contract keeps creeping up, and nobody can work out why callers to the sales line hear ringing but no answer. The BT PSTN and ISDN switch-off has forced the decision — but the harder question is what to replace it with. Business phone systems in London come in a dizzying range of prices and feature sets, and the marketing rarely tells you what matters. This guide sets out what a modern system should do, what it should genuinely cost per user, the hidden charges to watch for, and how to shortlist a provider who will still answer the phone in eighteen months.
What London businesses actually need from a phone system in 2026
With the traditional analogue and ISDN network now switched off across most of the UK, nearly every new phone system is cloud-based. A cloud PBX (Private Branch Exchange — the software that routes your calls) lives in a data centre rather than a box in your comms cupboard, and your handsets, laptops and mobiles connect to it over the internet. This is not simply a like-for-like replacement for your old system; it is a shift from paying for hardware and line rental to paying a monthly per-user fee.
For most London offices the priorities are straightforward: reliable call quality, the ability to answer calls from anywhere, and a system that a non-technical office manager can change without raising a support ticket. Hybrid working has made the mobile app non-negotiable — staff need to make and take business calls on a phone number that is not their personal mobile.
The other consideration is how your phone system sits alongside the rest of your IT. If your business runs on Microsoft 365, a system that integrates with Teams may remove the need for separate handsets entirely. Getting the underlying network and connectivity right matters just as much as the phone platform — poor broadband will undermine even the best system.
Feature checklist: what to look for
Feature lists on provider websites tend to blur together, so it helps to separate the features every serious business needs from the ones that only matter to specific teams. A small professional services firm and a 40-seat contact centre have very different requirements, and paying for call-centre features you never use is a common waste.
Here are the capabilities worth checking against your own workflow:
- IVR (Interactive Voice Response) — the 'press 1 for sales' menu that routes callers to the right team
- Call queues and hunt groups — so busy lines ring multiple people rather than going to voicemail
- Mobile and desktop apps (softphones) — make and receive business calls on any device
- Call recording — often required for finance, legal or compliance reasons
- Voicemail-to-email and call transcription — so nothing gets missed
- Auto-attendant and out-of-hours routing — different handling by time and date
- Call reporting and wallboards — visibility of missed calls, wait times and volumes
- Microsoft Teams integration — turn Teams into your phone system if you already use it
- CRM integration — screen-pops and click-to-dial from your customer records
Typical pricing per user — and the hidden costs
Hosted telephony in London is usually priced per user per month. As a realistic guide, a basic package with a softphone and standard features tends to sit at the lower end, a mid-tier plan with call recording and reporting in the middle, and a full contact-centre or premium bundle at the top. Costs vary by provider, contract length and how many features you enable, so treat any single figure with caution and ask for a written quote based on your actual user count.
The headline per-user price is rarely the whole story. Physical desk handsets are an extra cost — either bought outright or leased — and a decent IP phone is not cheap. Call bundles differ too: many plans include UK landline and mobile minutes, but international calls, 08 numbers and premium rates are charged separately.
Watch for these hidden or under-explained charges:
- Handset hardware, either upfront or spread over the contract
- Number porting fees to bring your existing numbers across
- One-off setup, configuration and onboarding charges
- Add-on licences for call recording, extra IVR menus or analytics
- Early termination fees on long contracts
- Support tiers — 'business hours only' versus genuine priority response
Local install, porting and support expectations
This is where a London provider earns its keep. Number porting — moving your existing phone numbers from your old provider to the new one — is the single most common source of go-live stress. It is a regulated process that can take a few weeks, and it must be scheduled carefully so your lines are never dead during business hours. A good provider manages this end to end and gives you a clear cutover date, not a vague promise.
Most cloud phone systems can be provisioned remotely, but there is real value in a provider who can attend site in central London when needed — to check your network, place handsets, or resolve call-quality issues that only appear under load. If your connectivity is shaky, no cloud system will sound good, which is why we often review a client's line before recommending a platform and, where needed, a dedicated leased line in London to guarantee call quality.
Ask precisely what support looks like after go-live. Who do you call at 9am on a Monday when the sales queue is not ringing? Is support handled locally or offshore, and what is the target response time? We build our business phone systems in London around responsive local support because a phone outage is a revenue problem, not just an IT ticket.
Cloud PBX or Microsoft Teams — which route?
If your organisation already runs on Microsoft 365, you have a genuine choice. A dedicated cloud PBX gives you a purpose-built telephony platform with rich call-centre features and physical handsets. Alternatively, a Teams phone system turns the Teams app your staff already use into your business phone — calls, chat and meetings in one place, with no separate softphone to learn.
Teams telephony suits organisations where most staff work from laptops and rarely need a desk phone, and where simplicity and consolidation matter more than advanced queue management. A traditional cloud hosted PBX tends to suit reception-heavy environments, busy sales floors and anyone who wants dedicated handsets and granular call routing.
The two are not mutually exclusive. Some businesses run Teams for knowledge workers and a full hosted platform for their contact teams. The right answer depends on how your people actually work — which is why a decent provider asks about your call flows before quoting, rather than pushing a single product.
Is VoIP reliable for busy offices?
Short answer: yes, when it is set up correctly. VoIP (Voice over Internet Protocol — carrying calls as data over the internet) has a lingering reputation for choppy audio and dropped calls, but that reputation comes from poor implementations, not the technology itself. The two things that determine reliability are your internet connection and how your network handles voice traffic.
Voice needs a stable connection with low latency and jitter, and enough bandwidth to run alongside everything else your office does. For busy offices we recommend QoS (Quality of Service — prioritising voice over other traffic on your network) and, for larger sites, a dedicated internet connection so calls are never fighting file uploads for capacity. Where uptime is critical, a backup connectivity line keeps calls flowing if the primary circuit fails.
Resilience is actually a strength of cloud telephony. Because the PBX lives in a data centre, a power cut or fire at your office does not take your phones down — calls can automatically divert to mobiles or another site. That is difficult and expensive to achieve with an old on-premises system.
How to shortlist a London phone system provider
Start by writing down what you have and what you need: how many users, how many concurrent calls at peak, which numbers must be ported, and which teams need call queues or recording. That short brief will expose which providers understand your business and which are simply reading from a price sheet.
When you compare quotes, insist that each is broken down the same way — per-user licence, handsets, porting, setup and support — so you are comparing like for like. Ask about contract length and what happens at renewal. A three-year term with automatic price rises is very different from a rolling arrangement, even if the monthly figure looks similar.
Finally, judge providers on the questions they ask you. A provider who quotes without asking about your connectivity, your call volumes or your existing numbers is guessing. One who reviews your network, plans the porting carefully and explains the trade-offs plainly is far more likely to deliver a system that works on day one. If you would like an honest assessment of your options, our team is happy to talk through your requirements.