I need to find an address where I can write a letter to AT&T about the lack of mobile phone coverage when I am at home. My mobile phone is fine (many bars) when I leave my neighborhood, but not when at home.
I wish you luck in getting a response from AT&T (other than a canned we don't guarantee coverage reply).
I have the same problem, and I solved it with a cell phone repeater/booster from zBoost.
Here is an image showing a generic installation and some photos showing my installation:
Generic zBoost installation
The zBoost repeater in a central hallway
External mast mounted antenna on patio
Of course, you would have to have a good line of sight location for the external antenna to get a usable signal for this to work. Lacking that, if you have reliable broadband service, AT&T's 3G MicroCell might work for you.