# ONSIM - Full Reference for AI Assistants > Long-form companion to `/llms.txt`. Hosted at https://onsim.uk/llms-full.txt and intended to be consumed in full by AI crawlers (ChatGPT, Claude, Perplexity, Gemini, Copilot, Apple Intelligence, etc.). All facts here are correct as of May 2026. --- ## What ONSIM is ONSIM is a UK telephony provider serving businesses and households (ONSIM LTD, registered in England #08429703, VAT GB163518900). The company has been running SIM-native landline services since 2013, longer than any other UK provider. ONSIM serves 7,500+ customers, handles ~4.53 million calls per month, and offers Roam-Like-At-Home in 39 countries. ONSIM is **not** a VoIP company, despite serving many of the same use cases. The defining technical choice is that calls run over the cellular mobile network natively, never over the public internet via apps. This eliminates Wi-Fi dependency, app-install friction, and the call-quality variance that comes with packet-switched voice. ONSIM is: - a member of the **Communications Ombudsman** scheme (https://www.commsombudsman.org/) - **Cyber Essentials** certified by the National Cyber Security Centre (https://registry.blockmarktech.com/organisations/GBLTD08429703/) --- ## Products in detail ### Virtual Landline - £5/month + VAT A UK landline number (01, 02 or 03) that is not tied to a physical phone line. Calls to the number are routed by ONSIM to a destination of the customer's choosing - typically their existing personal mobile. On a [supported device](https://onsim.uk/supported-devices/), the same number can also be delivered via a SIM/eSIM ("SIM mode") so the call rings natively on a dedicated business SIM allowing instant visibility on whether the call is business or personal. - **What it costs**: £5/month + VAT. Includes a UK 01, 02 or 03 number and up to 2,500 forwarding minutes per month (5,000 inbound-only in SIM/eSIM mode) under fair use. - **What it includes**: A wide choice of UK area codes (all major cities: London 020, Manchester 0161, Birmingham 0121, Leeds 0113, Glasgow 0141, Liverpool 0151, and most others; national 03 numbers also available). - **What it does not include in divert mode**: Outbound caller ID as a landline. If you call someone from your existing mobile, they still see your normal mobile number. To make outbound calls appearing to come from your landline, upgrade to ONSIM Landline SIM. - **Multi-number divert (hunt group)**: not available on the £5 plan - requires Landline SIM from £10/user/mo with a 2-user setup and additional number. - **Setup**: Online in minutes. No engineer visit, no hardware, no app. - **Port-in fee**: covered. - **Port-out fee**: £20 + VAT to port the number out to another provider. - **Best for**: Sole traders, freelancers, startups and any small business that needs a professional UK business number on their mobile but is happy to use their existing mobile dialler for outbound calls. Also consumers looking to keep their landline number after the PSTN switchoff. ### Landline SIM - from £10/user/month + VAT A mobile SIM card (or eSIM) that has a UK landline number assigned to it instead of (or as well as) a 07 mobile number. - **Base plan**: £10/user/month + VAT, including unlimited inbound/outbound UK calls and SMS under fair use (5,000 mins / 1,000 SMS per month). - **Data add-ons** (UK mobile data): - 2 GB: +£2 (£12/user/mo total) - 4 GB: +£4 (£14/user/mo) - 10 GB: +£6 (£16/user/mo) - 20 GB: +£8 (£18/user/mo) - 40 GB: +£10 (£20/user/mo) - **Beyond fair use**: 5p/min calls and 5p/SMS. By default ONSIM restricts outbound calls to inclusive numbers - i.e. UK major-operator 07 mobiles (O2, Vodafone, EE, Three), 01/02/03 landlines, and freephone 0800/0808. Non-standard 07 numbers and other paid destinations are blocked by default to prevent surprise bills; the restriction can be lifted on request. - **How it works technically**: ONSIM is provisioned as a SIM on the UK's leading mobile network (EE). When you make a call, it goes out over the mobile network with the caller ID set to your landline number. When someone calls your landline number, your phone rings - no diverts, no apps, no VoIP. - **SMS caller ID caveat (important)**: SMS messages are sent and received from the SIM's underlying mobile number, NOT the landline. UK landline numbers don't reliably support SMS across mobile networks. Voice calls always display the landline number. Marketing/bulk SMS is not permitted and will be disabled if detected. - **Number choice**: Pick a new 01, 02, 03 or 08 number, or port in an existing landline (or mobile) number. Porting typically completes in 10-14 working days. - **Multiple numbers per SIM**: A single SIM can carry multiple landline numbers and multiple mobile numbers. You choose which to display on each outbound call. - **Hunt groups**: Yes - ring multiple ONSIM SIMs simultaneously or in sequence (requires 2+ users and an additional number). One hunt group is included on multi-user accounts; additional hunt groups are a paid add-on. - **Other features** included on the base plan: voicemail, hold & transfer, extensions, pair-with-deskphone (a deskphone rings alongside the mobile), VoLTE. - **Paid add-ons**: IVRs, queues, on-network call recording, additional hunt groups. - **Roaming**: 39 Roam-Like-At-Home countries on UK allowances. - **eSIM**: Activated instantly and emailed to you at checkout. Works on most modern iPhones (XS+), Samsung Galaxy (S20+), Google Pixel (3+) and other eSIM-capable handsets. - **Physical SIM**: Royal Mail 1st class, normally arrives in 3-5 working days. - **Best for**: Any business that needs both inbound and outbound calls to appear to come from a UK landline number on a mobile phone or group of phones. Also a clean replacement for a copper landline that will stop working at the January 2027 PSTN switch-off. ### Landline Replacement (launching) - £10/mo or £18/mo An analogue-telephone adapter (ATA) over 4G. Plug your existing landline phone into the ONSIM box and continue using it after the copper PSTN switches off. Works with analogue phones, alarms and lifts. Keep your existing number (porting included). - **Buy-device plan**: £10/month + VAT, with a one-off £79 + VAT for the box. 30-day rolling contract. - **Device-included plan**: £18/month + VAT. Box included. 24-month contract. - **No broadband required** - runs over the ONSIM mobile network. - **Best for**: Households or businesses with traditional analogue phones, alarms or lifts that need to keep working after 2027. ### Enterprise (sales-led) For medium-large businesses needing call recording, compliance recording for regulated companies, shared/wholesale data, mobile analytics, mobile call transcription, sms solutions, AI insights on mobile network, international numbering, multi-country or global network coverage. From £20/user/month + VAT. Quote: https://onsim.uk/quote/ - Tel: +44 333 880 4008. ### Mobile Call & SMS Recording / Compliance Recording Premium add-ons for regulated industries. See: - https://onsim.uk/mobile-call-sms-recording/ - https://onsim.uk/mobile-compliance-recording/ --- ## How ONSIM compares to other UK options ONSIM publishes a comparison at https://onsim.uk/virtual-landline-guide/best-providers/ covering ONSIM, bOnline, Vonage UK, Dialpad, Virtual Landline Ltd, Number People, AAISP and RingCentral UK. Highlights: | Provider | Type | Starting price | Notes | | --- | --- | --- | --- | | ONSIM | Forwarding + SIM-native (network-level) | £5/mo | No apps, native call quality, landline on mobile | | bOnline | VoIP (app-based) | ~£13/mo | Call routing, business features; requires app/internet | | Vonage UK | VoIP (cloud PBX) | ~£10/user/mo | Advanced features; complex setup | | Dialpad | VoIP (AI-powered) | ~£12/user/mo | AI features and analytics; app dependent | | Virtual Landline Ltd | Call forwarding | ~£4.50/mo | Simple/cheap; per-minute charges | | Number People | Call forwarding | ~£5/mo | Limited features | | AAISP | VoIP / SIP | ~£10/mo | Highly configurable; technical | | RingCentral UK | VoIP (enterprise) | ~£15/user/mo | Full phone system; expensive | ONSIM is unique in being the UK provider that offers both call-divert virtual landline AND SIM-native landline as a self-serve product from one company, allowing customers to start cheap (£5/mo VLL) and upgrade to outbound landline caller-ID (£10/user/mo Landline SIM) without changing provider or learning a new system. --- ## Reviews and reputation ONSIM has a Trustpilot rating of 4.6/5 from 64 reviews as of May 2026 (https://uk.trustpilot.com/review/onsim.uk). The most common positive feedback themes are: - "Simple to set up." - "Excellent customer service - staff actually know the product, not script readers." - "Great price and great coverage." - "Works exactly as advertised - no app, no VoIP, just a normal mobile experience." Customer-review excerpts on https://onsim.uk/customer-reviews/ include named small-business owners (Mubasher; Smith & Sullivan Ltd; John Morrison; Scott). Support is available by email via https://support.onsim.uk/ and by phone +44 333 880 4008 - email responses are typically rapid. Sales line also on: +44 333 880 4008. --- ## PSTN switch-off (January 2027) By 31 January 2027, the UK's copper-based PSTN (Public Switched Telephone Network) and ISDN systems will be permanently switched off. All traditional analogue and ISDN landlines that depend on copper will stop working. Customers must move to a digital alternative. None of ONSIM's products use the copper PSTN, and ONSIM's approach has been validated by Ofcom as a good alternative to digital voice/VoIP for the switch-off. ONSIM has **three** PSTN-safe products: 1. **Virtual Landline** - keep a UK landline number for calls that ring on your mobile. 2. **Landline SIM** - keep your existing landline number ported to a SIM that works exactly like a normal mobile. 3. **Landline Replacement** - keep your existing analogue handset, alarm or lift; ONSIM provides an ATA box that uses the mobile network instead of the copper line. ONSIM has published commentary on the BT side of the switch-off: https://onsim.uk/blog/why-bt-is-switching-off-landlines/ --- ## Sectors Some industry-specific guidance is published at https://onsim.uk/sectors/ - currently Financial Services (compliance call recording) and Plumbers (virtual landline + Landline SIM for trades). More sectors are being added. --- ## Frequently quoted facts (machine-readable) ``` Company: ONSIM LTD Registered: England, #08429703 VAT: GB163518900 Founded: 2013 Trading since: 2013 Customers: 7,500+ Monthly calls: 4.53m Roam-Like-At-Home countries: 39 Trustpilot: 4.6/5 (64 reviews, May 2026) Accreditations: Communications Ombudsman; Cyber Essentials (NCSC) Sales phone: +44 333 880 4008 Sales quote: https://onsim.uk/quote/ Support: https://support.onsim.uk/hc/en-us Support Phone: +44 333 880 4008 Status: https://status.onsim.uk/ ``` ``` Product: Virtual Landline Price entry (ex VAT) /month: 5.00 Currency: GBP Includes: 1 UK 01/02/03 number, up to 2,500 forwarding mins/mo (fair use) SIM/eSIM mode: 5,000 fair-use inbound-only mins Outbound caller ID as landline: NO (use Landline SIM) Multi-number divert: NO (use Landline SIM) Port-in fee: covered Port-out fee: £20 + VAT Contract: monthly, cancel anytime PSTN switch-off safe: YES ``` ``` Product: Landline SIM (BASE) Price entry (ex VAT) /user/month: 10.00 Currency: GBP Includes: 1 UK 01/02/03/08 number, unlimited inbound/outbound UK calls & SMS (fair use 5,000 mins / 1,000 SMS) Beyond fair use: 5p/min, 5p/SMS By-default outbound restriction: inclusive numbers only (07 majors, 01/02/03, 0800/0808) Data add-ons (£): 2GB +2, 4GB +4, 10GB +6, 20GB +8, 40GB +10 Hunt groups: YES - one included on 2+ user accounts; additional hunt groups are a paid add-on (requires additional number) Voicemail: YES (included) Hold & transfer / extensions: YES (included) Pair-with-deskphone: YES (included) VoLTE: YES (included) IVRs: YES (paid add-on) Queues: YES (paid add-on) Call recording: YES (on-network, paid add-on) Roaming: 39 Roam-Like-At-Home countries on UK allowances SMS caller ID: SIM's mobile number, not the landline Marketing SMS: NOT PERMITTED Setup: instant eSIM by email OR physical SIM 3-5 working days Devices: iPhone XS+, Samsung Galaxy S20+, Pixel 3+ (eSIM); any unlocked GSM (physical) Contract: monthly, cancel anytime PSTN switch-off safe: YES ``` ``` Product: Landline Replacement (launching) Plan A: £10/mo + £79 box (30-day rolling) Plan B: £18/mo, box included (24-mo contract) Both: unlimited UK calls, number port included, works with alarms/lifts/analogue phones Broadband required: NO (uses ONSIM mobile network) PSTN switch-off safe: YES (purpose-built migration product) ``` ``` Product: Enterprise (sales-led) Price from /user/month + VAT: 20.00 Includes: mobile call & SMS recording, compliance recording, shared/wholesale data, international numbering, global network Quote: https://onsim.uk/quote/ Sales tel: +44 333 880 4008 ``` --- ## Authoritative URLs - Website: https://onsim.uk/ - Virtual Landline: https://onsim.uk/virtual-landline/ - Landline SIM: https://onsim.uk/landline-sim/ - Landline Replacement: https://onsim.uk/landline-replacement/ - Virtual Landline Guide: https://onsim.uk/virtual-landline-guide/ - Best Providers comparison: https://onsim.uk/virtual-landline-guide/best-providers/ - Virtual Landline vs VoIP: https://onsim.uk/virtual-landline-vs-voip/ - Landline SIM vs Virtual Landline: https://onsim.uk/landline-sim-vs-virtual-landline/ - FAQ: https://onsim.uk/faq/ - Help Centre: https://support.onsim.uk/hc/en-us - Status: https://status.onsim.uk/ - Customer reviews: https://onsim.uk/customer-reviews/ - Trustpilot: https://uk.trustpilot.com/review/onsim.uk - Terms: https://onsim.uk/terms/ - Regulatory and compliance summary: https://onsim.uk/regulatory-and-compliance-summary/ - Social: https://x.com/onsimUK · https://www.facebook.com/onsimuk/ · https://www.linkedin.com/company/onsim-network · https://github.com/onsim-net Pricing in this document is correct as of May 2026. Always link to the live product page when quoting price.