I’ve had EE from when they started and took over my previous provider which was orange I think, I’ve been to sites from as far as mablethorpe and down to Cornwall, I also use my mobile to set up telematics on vehicles and can be anywhere within a radius of 150 miles from home, the majority are in rural locations and in all the time I’ve been with EE I’ve had at most a half dozen times with no signal, I think EE use there own masts and also have use of BT I think and they certainly will going forward as EE and BT are now connected in some way I believe, but it’s good that all these other providers exist because if we all went to the same one there’d be no competition and prices would go up, we get a good deal with EE due to NHS discounts they offer to NHS staff, I rely heavily on my mobile which is why I have my main phone on EE and always have a backup which is a tesco, the tesco has been in my car for a couple of years and has never been switched on, but as has been said before each to their own, how much worse would lockdown have been with our mobiles.
BP
Have you tried your Tesco phone lately? Tesco runs on the O2 network - they are what is known as a MVNO or Mobile Virtual Network Operator - but still have to comply with O2 rules which on PAYG requires at least one chargeable event every 6 months. I suspect you will find it no longer works and your number may even have been re-issued to someone else. Oh, and you will have lost any credit on the account.
Now to expound upon how cellular works. There are four network operators in the UK, Vodafone, O2, 3 and BT/EE. EE came about when France Telecom who owned Orange and 1-2-1 that had long since become T-Mobile and were owned by Deutsche Telekom agreed to merge as EE or Everything Everywhere. EE was bought by BT just under five years ago but still operates as two separate mobile service providers on the same (EE) infrastructure.
3 and T-Mobile set up a joint network distribution company in 2007 called MBNL - Mobile Broadband Network Ltd - to get their networks to the radio sites by fibre or (in most cases) by microwave link. MBNL stayed in place when the EE merger and then the BT takeovers occurred. Not to be outdone VF and O2 set up the Cornerstone project to do the same for their networks. The outcome is that VF and O2 are mainly on the same sites (as in towers though not necessarily on street poles) and 3 and EE do the same on their sites although the sites may be owned by any of the cellular operators and shared, or be on sites owned by other organisations such as Arqiva. In some remote areas - such as the very rural parts of the Scottish Highlands - OfCom have given permission for local roaming to exist so that coverage can be improved by erection of single masts or use of existing sites that are not primarily cellular - such as TV/radio broadcast sites, microwave link sites, and mast sites owned by the emergency services and public authorities and utilities and saving cost in the process.
The problems of the different providers is about frequencies used. 3 used to have backup agreements with other providers (VF at first, later O2) for areas where they had no coverage, but a few years ago they decided their coverage (note population, not geographical) was good enough and cancelled the agreements. 3 operates solely in the 3G band around 2110MHz which suffers more rapid signal loss with distance so they need more sites. EE operates in the 1800MHz band and suffers the same issues to a lesser degree, but VF and O2 operate around 900MHz which suffers even less, these being 2G operations. 800MHz has been allocated for wide area 4G use for all providers although EE first started 4G also in the 1800MHz band. 5G when it arrives (for wide area) will be in the 700MHz band.
IME the problem with EE is that their sites hang on to a call until grim death, and then when it is handed on to the next cell there are no resources available so the call is dropped. O2 and VF do suffer the same but to a considerably lesser extent. EE is also expanding its 4G network as the new Emergency Services Network that will replace Airwave in the next year or so (in theory at least!) and the ESN needs geographical rather than population coverage.