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ONSIM vs Yay.com: SIM-native landline or VoIP phone system?
Both are UK business phone providers - but they solve different problems. Yay.com is a full cloud-VoIP phone system: apps, desk phones, IVRs, queues and team features over the internet. ONSIM delivers a landline number natively over the mobile network: no app, no VoIP, no broadband dependency.
This page is a fair side-by-side. Pick the one that fits your business, not the louder marketing.
Side-by-side
All prices ex VAT. Yay.com plan pricing couldn't be verified in July 2026 (rendered in-app) - check yay.com live before deciding.
| ONSIM | Yay.com | |
|---|---|---|
| What it is | SIM-native landline + call divert | Cloud-VoIP phone system (hosted PBX) |
| Delivery | Mobile network - SIM/eSIM or divert | Internet - apps, browser, IP desk phones |
| Requires app | No | Yes (softphone) or IP desk phone |
| Requires broadband/internet | No | Yes |
| Entry price | £5/mo + VAT (Virtual Landline) | Not verified - check yay.com |
| With outbound landline CLI | £10/user/mo + VAT (Landline SIM, native) | Included in VoIP plans (via app/handset) |
| IVR menus, queues, extensions | Extensions included; IVR/queues paid add-ons | Core product - rich PBX feature set |
| Desk phones | Pair-with-deskphone included | Full IP desk phone support |
| Call quality during broadband outage | Unaffected (mobile network) | Calls stop (unless app on mobile data) |
| PSTN switch-off-safe | Yes - plus analogue Landline Replacement box | Yes (uses internet) |
| Trading since | 2013 (SIM-native landline) | Established UK VoIP provider |
| Trustpilot | 4.6/5, 64 reviews | Reviewed on Trustpilot - check live rating |
When ONSIM is the better choice
- Your team is mobile-first - vans, sites, client visits, remote work
- You want zero app friction: the landline number rings and dials from the phone's normal dialler (Landline SIM)
- Call quality must not depend on Wi-Fi or broadband
- You want a cheap £5 starting point with a £10 SIM-native upgrade under one provider
- You're replacing a copper line ahead of January 2027, possibly keeping analogue phones (Landline Replacement)
When Yay.com is the better choice
- You need a genuine multi-user phone system: extensions, IVR menus, call queues, conferencing
- Your team is desk-based with reliable broadband and you want IP desk phones
- You value a polished, developer-led VoIP platform with strong apps and admin tools
- You want deep PBX configurability as the core product rather than as add-ons
More about Yay.com at yay.com.
Frequently Asked Questions
Common questions before choosing between the two.
What's the main difference between ONSIM and Yay.com?
They are different categories of product. Yay.com is a UK cloud-VoIP phone system: calls run over the internet through softphone apps, browser clients and desk phones, with PBX features like IVR menus, call queues, hunt groups and music on hold. ONSIM is SIM-native: a UK landline number delivered over the mobile network - either as a £5/month divert or a £10/user/month Landline SIM where the number lives on the SIM itself. No app, no VoIP, no broadband dependency.
How does pricing compare?
ONSIM Virtual Landline is £5/month + VAT; ONSIM Landline SIM is £10/user/month + VAT with unlimited UK calls and SMS (fair use). We couldn't verify Yay.com's current plan prices when we checked in July 2026 (their pricing renders in-app) - their published entry pricing has historically been competitive for VoIP, typically a few pounds per user per month on annual billing - check yay.com for live prices before deciding.
Does either need an app or broadband?
Yay.com is VoIP, so calls need an internet connection and run through their apps, browser client or an IP desk phone - that's inherent to the category, and their apps are well regarded. ONSIM needs neither: on the Landline SIM the landline number is on the SIM, so calls use the phone's normal dialler over the mobile network. If broadband goes down, ONSIM calls are unaffected.
When is Yay.com the better choice?
Pick Yay.com if you need a proper multi-user phone system: extensions for a team, IVR menus, call queues, conferencing, desk phones on desks, integrations and centralised admin. Yay.com is a developer-led UK provider with a polished platform, and a VoIP PBX is the right architecture for a desk-based team with reliable broadband. ONSIM doesn't try to be a full PBX - IVRs and queues exist but as paid add-ons, not the core product.
When is ONSIM the better choice?
Pick ONSIM if your business lives on mobiles rather than desks. The Landline SIM gives every user a landline number that rings and dials natively - no softphone to keep logged in, no Wi-Fi variable, no headset. It suits trades, field teams, consultants and anyone replacing a copper line ahead of the January 2027 PSTN switch-off - including with the plug-in Landline Replacement box for analogue phones.
Can I keep my number if I switch either way?
Yes. UK number portability is mandatory and both providers support porting. ONSIM ports most UK landline numbers in within 10-14 working days; port-in is included on Landline SIM (one-off £20+VAT on Virtual Landline) and the port-out fee is £20+VAT.
Which is more reliable for call quality?
Different failure modes. Yay.com's quality depends on your internet connection - excellent on good broadband, variable on congested Wi-Fi or mobile data. ONSIM calls are circuit-switched mobile calls on the EE network (with VoLTE), so quality is the same as any normal mobile call and never touches your broadband. If your team works from vans, sites or patchy-Wi-Fi locations, that difference is the whole decision.