Most recent advice from AT&T for iPhone 4 (assuming 3G, 3Gs, and 4Gs) and MicroCell connectivity.
Unplug MicroCell for 30 seconds.
Plug it back in.
Turn off iPhone for 30 seconds.
Turn it back on.
Reset Network Settings on iPhone. (Under Settings -> General -> Reset Network Setting) This will cycle the iPhone (turn it on and off automatically) WARNING: Resetting this will require you to rejoin your network (if wireless) and to re-enter your password for the network. Make sure you have it before you do this!!!
Wait until Friday when AT&T will call me back and explain why the iPhone won't force connect to the MicroCell when I get back to my house. Or when a random 1 bar of edge network signal is picked up and permanently disconnects it.
At the end of the day, the only success I've had is putting your phone into Airplane mode for a second and then turning Airplane mode off.
Take it or leave it, this is the best I've got right now.
