Free tools
Free UK telecoms tools
Data-backed tools we built while working on our own telephony products. All free, no sign-up, no data captured about your lookups. Underlying data comes from Ofcom, Openreach and other public sources, used under the Open Government Licence.
Number lookup
UK Phone Number Checker
Who called me? What type of number is this?
Paste any UK phone number. See what type of number it is (landline, mobile, freephone, premium), what area it is from, and which network operator was originally allocated the block. All formatted variants (national, international, E.164). Uses Ofcom's official numbering data.
Source: Ofcom Numbering Data + Ofcom Area Codes Tool
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Number lookup
Network Lookup
Which network is this phone number on?
Enter any UK phone number, especially an 07 mobile, to see which network the number range was originally allocated to (O2, Vodafone, EE, Three and hundreds more). Honest about the limits: ported numbers may now be on a different network, and we say so on every result. Uses Ofcom's official numbering data.
Source: Ofcom Numbering Data
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Switch-off planning
PSTN Switch-Off Checker
Am I affected by the January 2027 switch-off?
Answer 5 short questions about your phone, broadband and equipment. Get a personalised verdict on whether the PSTN switch-off affects you, what specifically stops working, and ranked replacement options with honest trade-offs.
Source: Openreach + industry sources
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Compliance
Call Recording Retention Calculator
How long must I keep call recordings?
3 questions. Get the minimum retention period across UK regulatory regimes (FCA SYSC 10A, MiFID II, PCI DSS, MLR 2017, SRA, ICOBS, UK GDPR, FOS). Every rule cited to its source. Built for compliance officers.
Source: FCA Handbook + UK legislation + PCI SSC
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Number choice
Business Number Chooser
What type of phone number should my business choose?
Answer 6 quick questions about your customers, your brand and who should pay for calls. Get a recommendation between local 01/02, national 0330/0333, freephone 0800 and 0300 numbers, with an honest alternative, the real cost trade-offs (including the 0800 inbound charge), and the porting path if you already have a number.
Source: Ofcom number ranges + ONSIM pricing
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Device compatibility
eSIM Compatibility Checker
Is my phone eSIM compatible?
Pick your phone from 222 UK-market devices across 12 brands. Two separate answers per model: does the phone support eSIM at all (with dual-eSIM and regional caveats), and is it supported on the ONSIM network? Includes the universal *#06# EID test for phones not in the database. Verified against manufacturer and UK carrier sources.
Source: Manufacturer spec pages + UK carrier eSIM lists
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Compliance
Call Recording Requirement Checker
Do I need to record calls at all?
Answer 5 quick questions about your firm. Find out whether the FCA taping rule (SYSC 10A) applies to you, whether recording is strongly advisable anyway (SYSC 9, Consumer Duty, PCI DSS, FOS), or whether no regulatory driver exists. Built for IFAs and mortgage / insurance brokers.
Source: FCA Handbook + FCA policy statements + PCI SSC
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Why we build these
ONSIM is a UK telephony provider running since 2013. We build tools like these while working through the same questions our customers ask us: is this number a scam? What area code will I get if I move? Does the PSTN switch-off affect me? The public data is out there but it is hard to use.
Each tool uses real underlying data (Ofcom's official numbering plan, Openreach's rollout, our own MVNO experience) rather than heuristics or LLM-generated content. Where we do not have the data to answer confidently, we say so.
If you spot a mistake, please let us know. If a tool would help you and we do not have it, tell us that too.
Looking for a paid ONSIM product?
Virtual Landline (£5/mo), a UK landline number that rings your mobile. Landline SIM (from £10/user/mo), a mobile SIM with a landline number. Landline Replacement (from £10/mo), a copper-PSTN drop-in for the 2027 switch-off. See all products on the homepage.