CA's comment about the coverage checkers I have to echo, where I live, I am supposed to be in a very good coverage area for two of the networks, yet step inside my front door and the signal becomes useless for voice usage, and even texts are temperamental, yet a network which reports me to be in a poor area works better than the two good ones, though I still have to stand leaning over the kitchen sink to get a usable voice signal.
I was talking to a guy who works for one of the large energy suppliers. He was telling me that the roll out of smart meters is being hampered by the availability of mobile phone signals. Their company has had to bring in a second more expensive supplier of meters which have a better signal reception to be fitted in areas with difficult reception. There re still some places where smart meters simply will not work becasue of the lack of signal.
Something else that surprised me was that the smart meter is still presently company specific, if you change providers, many will need your meter changing, though there are moves afoot that should simplify the process to just changing a sim card, though that will still apparently require an home visit.