Advisory note AN-13Joining a network
The order in which a network should be chosen, and the four things to do on your first day of service.
Note AN-13 · four sections · reviewed July 2026 · no prices published
Independent status. fernwick is an independent guidance and information service. We are not a mobile network. We are not affiliated with, endorsed by, appointed by or connected to Three, EE, O2, Vodafone, Sky Mobile, Tesco Mobile or any other provider, and we hold no commercial arrangement with any of them. We do not sell, supply, arrange or broker SIM cards, contracts, handsets or services of any kind, and we take no commission. Everything published here is general information and must not be relied upon in place of the provider's own current terms.
Our position in one lineCheck coverage first and price last — reversing that order is the most expensive habit in British mobile.
§1Check before you buy
Run the provider's own postcode checker and Ofcom's independent one, weighting the indoor predictions most heavily. Coverage maps model outdoor signal, and you live indoors.
Where the two disagree, a test month decides. What no map can show you at all is your own building materials, or how many handsets share your local mast at six in the evening.
If any of this is unclear
Telephone the advisory and we will talk it through. There is nothing to buy at any point.
020 3896 5248This line is for guidance and information only. We sell nothing, arrange nothing and act for no provider. If anything on this page is unclear, telephone and we will explain it. §2The test month
A rolling monthly SIM on the intended masts costs very little and answers the only question that matters.
| Network you are testing | Cheapest way to test it |
|---|
| O2 | giffgaff or Tesco Mobile |
| Three | SMARTY or iD Mobile |
| EE | 1pMobile |
| Vodafone | VOXI or Lebara |
Live on it through an ordinary week rather than a good one: home, work, the journey, the supermarket queue — and the rooms you actually occupy, at the hours you occupy them.
§3Bringing your number in
Buy the new plan first.
Request the free code from your outgoing provider by text.
Give the code to the new provider.
Keep the old SIM in the handset until the number transfers — usually one working day, with no gap in service.
§4Four things on the first day
- Wi-Fi Calling on. Calls travel over your broadband, so walls stop mattering. Free, and switched off by default on plenty of handsets.
- 4G Calling on. This is how voice travels now that 3G has closed on every UK network.
- Spend cap set. Free, about a minute, and the main defence against charges beyond the allowance.
- End date diarised. If you took a fixed term, this single note is worth more than any comparison site.
Common pitfallGenuine offers only ever appear inside your provider's own app. That is how you check whether any caller is real — and no genuine agent ever needs a one-time code read aloud.
Speak to the advisory
Telephone the advisory and we will talk it through. There is nothing to buy at any point.
020 3896 5248This line is for guidance and information only. We sell nothing, arrange nothing and act for no provider. If anything on this page is unclear, telephone and we will explain it. Independent status. fernwick is an independent guidance and information service. We are not a mobile network. We are not affiliated with, endorsed by, appointed by or connected to Three, EE, O2, Vodafone, Sky Mobile, Tesco Mobile or any other provider, and we hold no commercial arrangement with any of them. We do not sell, supply, arrange or broker SIM cards, contracts, handsets or services of any kind, and we take no commission. Everything published here is general information and must not be relied upon in place of the provider's own current terms.