- Go to your phone keypad.
- Dial: *3001#12345#*
- Press "Call."
For example, I tested my 3G signal strength at work today. It ranged from -71 to -77. My EDGE signal ranged from -69 to -73. The closer you get -50 the better your reception. The closer to -100 the worse your signal is.
This is helpful especially when an article like this was published recently: Fewer Bars in More Places: AT&T Network Upgrades Degrade Service for 2G Phones