Sure SIgnal/Home Signal
While they have their failings, I'll give Three their due. It took all of about 30 minutes to agree that the signal indoors was non-existent - it didn't even have enough ummph to qualify as pants. Once that was agreed, it was a quick hop and a skip to securing their Home signal which backhauls over the broadband - and as the rest of the family are on Three as well, they can all be registered on the same device. Result - 4 bars indoors.
Changed SIM recently - and when that didn't sign on, a quick call to Three support and 5 minutes later it was sorted - the registration on the Home signal is via the SIM ID.
All in all - it makes them usable.