Wired’s How-To Wiki has a nice step-by-step walkthrough that tells you how to get the most out of your cellphone’s signal.

Obstructions like walls, mountains and fat people; RF interference; weather; and your phone’s antenna placement are all things than can dilute your signal to a tiny, staticky trickle.

Here are recommended fixes:

1. Change Location: If possible shift
2. Get An External Antenna: An external antenna works when your internal one cant do the job
3. Invest In A Repeater: A repeater gets weak signal and boosts it for your phone
4. Change The Way You Hold The Phone: Yes, surprisingly the way you’re holding the gadget could make substantial difference to the signal

If none of these work you probably need to call up your provider, threaten them with a switchover and hope someone listens and sets up a cell tower next door.