Remember mobile phone technology seems to get weaker with each new model, prime example being Bluetooth. Early Bluetooth phones like the Nokia 6310 where very strong and would talk to just about anything. Todays Bluetooth phones are inferior, this is a big problem when trying to sell a car with Bluetooth, try explaining to someone that there all singing all danceing Blackberry is piss all use with £70k's worth of Range Rover. Goes down a treat, trust me ;)Back on subject... dont buy any of the boosters you see on Ebay, I have bought and sold a few in bulk in the past to make a few quid, they make no difference at all I'm afraid.
Where I live all mobiles are patchy, I'm with Orange mainly because I like to be a loyal customer and they have very good back up. Through experience if I leave my phone on an upside down glass on the kitchen table it gets a signal. No idea why but it works for me!! :D