Switching from 3G to Edge (2G)

I am hoping someone can help me.  I just purchased 2 Xenon's and they work great away from my home.  In my home it won't receive any text messages and its tough to keep a call going without it dropping off.  I also have an iPhone and have to switch from 3G to 2G in order for me to use voice and to send and receive text messages.  I assume that I just don't have enough signal for my phones to utilize 3G.   Does anyone know how to change from 3G to EDGE?  I know the phone is suppose to change automatically when the signal is not strong enough, but that does not happen either.  It looks as though there is enough signal strength to keep it 3G but not work very well.  Any insite would be greatly appreciated.  Thanks, RK