Choosing the right business phone system: an honest 2026 buyer's guide

A UK business buying a phone system in 2026 has three real options. They're sold under a confusion of names ("UCaaS", "cloud telephony", "virtual PBX", "digital voice for business", "3CX on-prem"), but the underlying architecture comes down to three patterns:

• On-premise PBX — you own the box, it sits in your comms cupboard, you (or a maintainer) keep it running.
• Hosted cloud PBX — the PBX lives in a data centre, your phones register to it over the internet.
• Pure softphone / app-only — no PBX at all, users get an app on their phone or computer.

This is an honest buyer's guide. Which one suits which business, what each costs end-to-end (not just the headline), and the questions to ask before you sign. No vendor fluff, no "and that's why our product is best."

Option 1: on-premise PBX

A physical box (or a Linux server) in your comms cupboard handles all the call logic. Each desk phone plugs into your LAN, registers to the PBX, and the PBX talks to the outside world via SIP trunks (or, increasingly rarely, ISDN).

Who it suits

• Businesses with a strong in-house IT team that already runs Linux.
• Sites where compliance or sovereignty matters (full control of every recording, no calls leaving the building).
• 3CX-licensed installs that have already amortised the licence cost.
• Setups with bespoke routing rules or CRM integrations that need direct PBX access.

What it costs

• Up-front hardware: £1,500–£10,000 depending on size.
• PBX software / licence: £200–£3,000/year (3CX, Mitel, etc.).
• SIP trunks: needed separately. With Membership, included.
• Maintenance: either a tame Linux admin, or a managed service contract at £100–£500/mo.
• Replacement cycle: every 5–7 years.

The honest downsides

You're running infrastructure. Software updates, security patches, certificate renewals, hardware failures, the whole ops burden. If the PBX goes down at 8am Monday, you're the one fixing it. Most SMEs that move away from on-prem cite this as the deciding factor.

Option 2: hosted cloud PBX

The PBX itself lives in a carrier-grade data centre. Your desk phones, softphones and SIP trunks register to it over the internet. You get an admin web portal to configure routing, IVR menus, hunt groups, voicemail, call recording. Updates happen automatically; nothing in your office to maintain.

Who it suits

• The default answer for most UK SMEs — 90%+ of businesses migrating off ISDN go here.
• Hybrid teams (some in-office, some remote, some on mobile).
• Businesses that want every smart feature without paying per bolt-on.
• Anyone replacing a legacy PBX past its 7-year mark.

What it costs

With NumberGroup Membership, the full hosted-PBX stack is £149/month flat — no per-user fee, no per-feature bolt-on. That includes up to 25 concurrent calls, unlimited UK numbers, hosted PBX with every smart feature, SIP trunks, port-in of existing numbers, and a UK team. Per-call rates are wholesale (~0.3p/min landline, ~0.6p/min mobile).

Desk phones (if you want them) are supplied at our distributor cost — no handset markup. Grandstream GXP1625 £28, GXP2135 £64, GXP2170 £83 ex-VAT.

The honest downsides

You depend on your internet connection. If the office WAN goes down, the office phones go down (though calls can re-route to mobile automatically — try doing that on an ISDN line). For businesses on slow ADSL, upgrade the broadband first.

Option 3: pure softphone / app-only

No PBX, no desk phones. Each user gets a softphone app on their laptop or mobile. Calls land wherever they're logged in.

Who it suits

• 1–3 person businesses with no office.
• Fully-remote teams where everyone's on a laptop.
• Side projects and very early startups that want a business number with no setup.

What it costs

With Membership, our branded Acrobits softphones are ~75p per active install, billed monthly. You can mix softphones with desk phones on the same Membership.

The honest downsides

Notifications get missed, headset quality varies, and customers can sometimes hear the difference between a softphone and a desk phone on a poor laptop mic. If inbound is mission-critical, buy desk phones for the office and use softphones as backup.

Six questions to answer before you choose

1. What setup are you using today?

If you're still on ISDN, the deadline is 31 January 2027. Stop-sell already happened, so you can't renew. If you've already got a SIP-capable PBX less than 10 years old, keeping it and just swapping the trunks usually costs less than ripping it out.

2. How many calls do you handle?

Total concurrent calls (not minutes per month) determines channel capacity. Membership includes up to 25 concurrent calls. Above that, talk to us — we don't do per-channel licence fees so the scaling answer is honest.

3. How much are you willing to invest?

On-prem has a five-figure up-front cost and ongoing maintenance. Hosted has zero up-front and a fixed monthly fee. For most SMEs, the 5-year total cost of ownership is 30–50% lower on hosted. For larger sites with existing PBX investments that aren't amortised yet, on-prem can still win.

4. How are your employees working?

Office-only and high-call-volume → hybrid of desk phones + a small softphone footprint. Hybrid teams → desk phones in the office, softphone everywhere else. Fully-remote → softphone only.

5. Which features matter?

The 2026 baseline every business should expect for free: IVR menus, hunt groups, time-of-day routing, voicemail-to-email, call recording, conference bridges, mobile + desk integration. Anyone pricing these as bolt-ons in 2026 is selling you a subscription that doesn't reflect the underlying cost.

6. How reliable is your internet?

VoIP needs ~100kbps per concurrent call plus low jitter. Standard FTTC (80/20) handles most small offices comfortably. FTTP is better if you can get it. Bonded ADSL or 4G are adequate fallbacks. If you're on legacy slow ADSL, upgrade the broadband before the voice migration.

The honest recommendation

For 90% of UK SMEs in 2026: hosted cloud PBX with SIP trunks at carrier cost. That's what Membership delivers, at £149/mo flat. No per-user, no per-feature, no minimum commit, no contract.

For the other 10% — established 3CX shops, businesses with specific compliance requirements, sites with sovereign-data needs — on-prem still has a place, and we'll happily supply the SIP trunks for it.