What phone system do you need? A guide by team size

The right phone system depends first on how many people will use it, then on how they work.

• One to four people: Gamma Phoneline+ or Gamma Horizon usually fits.
• Five to 24 people: Horizon is the most common answer. 3CX or Gamma Webex suit teams that need more.
• 25 or more: 3CX is our first recommendation.
• Very large or security-led organisations: Mitel MiVoice Business is worth a look.

T2K Voice & Data built the Phone System Finder around these questions. This guide shows the reasoning behind it, size by size, so you can see why a 10-person office gets a different answer from a one-person business. If you'd rather skip the reading, the finder asks seven questions and gives you a ranked shortlist and a comparison quote.

Which phone system suits each team size?

How does T2K's Phone System Finder choose a phone system?

The finder scores six systems against your answers to seven questions, then ranks them by best match. Every answer adds points to the systems that suit it, so no single answer decides the result.

The questions cover:

• team size
• what matters most (simplicity, features, cost or control)
• where the system is hosted
• how your team works
• how advanced your call handling is
• which business tools it needs to connect with
• your approach to budget

Phoneline+, Horizon, 3CX and Gamma Webex are our core four. Mitel MiVoice Business and Voiceflex Flow are specialist options, so they need a stronger, more specific signal in your answers before they outrank the core four.

Two rules sit on top of the scoring. Once you reach five users, the finder stops putting Phoneline+ first. Once you reach 25 users, it puts 3CX first. Phoneline+ is designed for very small teams. 3CX charges by concurrent calls rather than headcount, which tends to work out cheaper as a team grows.

What are the six systems the finder compares?

What phone system is best for a one-man band or sole trader?

For most one-person businesses, Gamma Phoneline+ is the right choice. It replaces a traditional landline without any hardware, keeps your existing number, and includes a mobile app, voicemail to email and unlimited UK calls. Activation can be the same day.

Picture a plumber in Leeds working from a van. Customers ring the business number, and the call lands on his mobile through the app. He never gives out his personal number, and there's no desk phone to plug in. If you're a tradesperson, our guide to phone systems for tradesmen goes further.

Phoneline+ has limits. It has no call recording, no CRM integration and no video conferencing. A sole-practitioner solicitor in Edinburgh who needs to record client calls should look at Horizon instead.

How the finder scores it: team size alone gives Phoneline+ four points and Horizon two. Answer "simple", "basic call handling" and "lowest cost", and Phoneline+ pulls well clear.

Related reading: what is a VoIP phone number? and keeping your number when you switch.

What phone system is best for a company with 3 staff?

Three staff still sits in Phoneline+ territory if your calls are simple. Move to Gamma Horizon once you want an auto-attendant, hunt groups (calls ringing several people) or call recording.

Take a three-person accountancy in Nottingham. If everyone answers their own calls and voicemail goes to email, Phoneline+ is enough. If clients should hear "press 1 for tax, press 2 for payroll" before reaching a person, Horizon is the better fit. It runs from a web-based admin portal, so you can change routing yourself without ringing anyone.

Very occasionally a three-person business wants a system in its own building. That's unusual, and 3CX is the natural fit if so, but a hosted system is nearly always less hassle at this size.

How the finder scores it: choose intermediate call handling (hunt groups, auto-attendant, hold music) and Horizon takes the lead. It earns four points there, while Phoneline+ earns none.

Not sure what the jargon means? Our A to Z of VoIP jargon explains it plainly.

What phone system is best for 5 staff?

At five staff, Gamma Horizon is the usual answer. It needs no on-site hardware, it has a strong mobile app, and it handles the call routing a small office needs without much administration.

Think of a five-person estate agency branch in Cardiff. Calls need to reach whoever is free, and out-of-hours enquiries shouldn't vanish. Our guide to call routing for estate agents shows how that works in practice.

The trade-off is that Horizon is cloud only, and Teams integration comes through an add-on. If your team lives in Microsoft Teams, ask us about Voiceflex Flow, a specialist option built around Teams.

How the finder scores it: five users still counts as a micro-business for scoring, so Phoneline+ can rank a close second when calls are basic and cost matters most. It won't be first at this size.

What phone system is best for 10 staff?

For 10 staff, there are three good answers, and your other answers decide between them.

• Gamma Horizon suits you if you want fully managed cloud telephony with no IT fuss.
• 3CX suits you if you want on-premises hosting, built-in video conferencing or deeper CRM links, and someone can help with setup.
• Gamma Webex suits you if your team works hybrid and you want voice, meetings and messaging under one licence, with AI transcription built in.

Imagine a 10-person dental practice in Sheffield. The front desk is busy, and nobody wants to manage a server. Horizon fits. Now imagine a 10-person consultancy in Manchester, working hybrid, with Microsoft 365 and a CRM. Webex closes the gap on Horizon, and it's worth asking us about Voiceflex Flow, which adds full phone system calling inside Teams without a Teams Phone licence.

How the finder scores it: select "Microsoft 365 / Teams and CRM" for integrations and Gamma Webex earns five points while Horizon earns none. That narrows the gap between them to a point or two.

We compare the two most common contenders in 3CX vs Gamma Horizon. If Teams is your main tool, read 3CX vs Microsoft Teams Phone.

What phone system is best for 20 staff?

At 20 staff, choose between Gamma Horizon and 3CX based on how much management you want. Horizon asks the least of you. 3CX gets more attractive because you pay per concurrent call rather than per person.

Most 20-person offices don't have 20 people on the phone at once. That gap is where 3CX's pricing model starts to save money. A 20-person law firm in Birmingham might also need call recording for compliance. Both systems offer it, and our guide to call recording compliance covers what to check.

How the finder scores it: choose "on-premises" hosting and both 3CX and Mitel earn five points. Choose "good value for the features" and 3CX and Horizon earn four each.

What phone system is best for 25 to 50 staff?

For 25 to 50 staff, 3CX is our first recommendation. It's priced by concurrent calls rather than per user, runs on-premises or in the cloud, and includes video conferencing, call queues and CRM integration.

It isn't right for everyone. 3CX works best with some IT support behind it, it's less hands-off than a fully hosted system, and it's sold on an annual licence. If nobody in your business enjoys IT, tell us, because Horizon may be the calmer choice.

T2K has delivered 3CX across nine care home sites, which shows how the platform copes with multiple locations. Our ultimate 3CX guide covers setup and pricing in detail.

How the finder scores it: the 26–100 band gives 3CX and Horizon three points each on size alone, so your other answers decide the runners-up. From 25 users, the finder always puts 3CX first.

What phone system is best for 100 staff?

At 100 staff, 3CX is still the first recommendation. Gamma Webex or Mitel MiVoice Business deserve a look if you run a contact centre, need strict compliance, or want AI-assisted meetings alongside voice.

A 100-person manufacturer with sites in Wolverhampton and Coventry has different needs from a single office. Multi-site call routing, CRM integration and reporting all start to matter. Read our guide to CRM phone system integration. If you're moving off an older system, 3CX vs Mitel may help.

How the finder scores it: answer "contact centre" for call handling and Mitel earns five points, while 3CX and Webex earn four each. Our call centre phone system guide goes deeper.

What phone system is best for 250 staff or more?

For 250 staff or more, the finder still starts with 3CX, and Mitel MiVoice Business is the alternative to weigh up. Mitel scales from 5 to 65,000 users on one platform. It runs on-premises, in a private cloud or in a public cloud, and offers CapEx or OpEx pricing.

That flexibility suits organisations with data sovereignty or compliance requirements, such as a multi-academy trust based around Newcastle. See our guide to multi-academy trust phone systems for that scenario.

Mitel has downsides. On-premises deployments cost more upfront, an IT resource is recommended, and there's no native Teams integration.

How the finder scores it: teams of 101 to 500 give Mitel four points on size alone, against three for 3CX and Webex. Above 500, that rises to five.

What else changes the answer besides team size?

Team size sets the starting point, but six other answers can move the result. Here's what pulls scores hardest:

• You want on-premises hosting: 3CX and Mitel earn five points each. Cloud-only systems earn none.
• You want to buy outright rather than subscribe: Mitel earns five points, 3CX four.
• You work fully remotely or across sites: Webex earns four points, 3CX and Horizon three each.
• You need Teams and CRM connected: Webex earns five points, 3CX and Mitel three each. Horizon earns none.
• You want the lowest monthly cost: Phoneline+ earns five points, 3CX three.
• You need full contact centre capability: Mitel earns five points, 3CX and Webex four each.

Wondering whether the cloud or on-premises answer is right for you? Our comparison of cloud, on-premise and hybrid phone systems will help.