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ONSIM vs Vonage UK: which is right for your business?
Both are UK business phone providers, but they're aimed at very different setups. ONSIM puts a UK landline number on your existing mobile via the mobile network - no app, no VoIP. Vonage UK is a full cloud PBX delivered through apps and desk phones, suited to teams that need rich call-management.
Side-by-side
All prices ex VAT. Vonage UK pricing checked May–June 2026; verify live before deciding.
| ONSIM | Vonage UK | |
|---|---|---|
| Delivery | Mobile network - SIM/eSIM or call divert | VoIP / cloud PBX - app + desk phones |
| Requires app | No | Yes (for mobile and desktop) |
| Requires broadband | No | Yes |
| Entry price | £5/mo + VAT (Virtual Landline) | ~£10/user/mo + VAT |
| With outbound landline CLI | £10/user/mo + VAT (Landline SIM) | Included in plan |
| Multi-user / hunt groups | Yes (one included on multi-user accounts) | Yes (rich routing built in) |
| IVRs, queues, conferencing | Paid add-ons | Included on higher tiers |
| CRM integrations | Via Developer API | Native integrations |
| Best for | Mobile-first SMBs, sole traders, trades, PSTN-replacement | Desk-based teams needing rich PBX features |
When ONSIM is the better choice
- You work mostly from a mobile and don't want an app
- You want the simplest possible setup - no PBX configuration
- You can't depend on broadband for call quality (rural, fringe coverage, field work)
- You're replacing a copper PSTN line ahead of 2027 (Landline Replacement)
When Vonage UK is the better choice
- You have a team of 5+ desk-based users on stable broadband
- You need a full cloud PBX with IVR menus and call queues
- You want native CRM integrations and built-in analytics
- You're standardising on IP desk phones across an office
More about Vonage UK at vonage.co.uk.
Frequently Asked Questions
Common questions before choosing between the two.
What's the main difference between ONSIM and Vonage?
ONSIM delivers a UK landline number natively over the mobile network - calls behave like a normal mobile call, no app, no VoIP. Vonage UK is a cloud PBX delivered through a desktop and mobile app, with extensive call-management features built for desk-based teams.
How does pricing compare?
ONSIM Virtual Landline is £5/month + VAT (inbound calls). ONSIM Landline SIM is £10/user/month + VAT (inbound + outbound landline CLI). Vonage UK typically starts around £10/user/month for entry tiers and rises with feature bundles. Verify Vonage pricing live before deciding - their UK tiers and packaging change.
When is ONSIM the better choice?
When you want a UK landline number on your existing mobile with no app, no VoIP, no broadband dependency. ONSIM suits sole traders, trades (plumbers, electricians), mobile-first SMBs, and anyone replacing a copper PSTN line without broadband (Landline Replacement).
When is Vonage the better choice?
When you need a multi-user cloud PBX with desk phones, advanced IVRs, call recording across the team, CRM integrations and analytics. Vonage is well-suited to medium-large desk-based teams with reliable broadband.
Can I run both?
Yes - some businesses use a Vonage PBX for the head office desks and ONSIM for field staff who want a landline number on their personal mobile without an app. They serve different parts of the same business.
Can I switch between them?
Yes. UK number portability is mandatory. ONSIM can port most UK landline numbers (~10-14 working days). Vonage similarly supports number porting. ONSIM port-out fee is £20+VAT.