I have an unlocked Xperia Play R800at. I know for a fact the phone signal in my area works because of my previous phone which never had a problem with signal. I don't have data (atm) so the only thing I'm trying to work is talk and messaging. The phone connects to the network but it constantly loses its signal. I tried changing the APN settings like My Family Mobile suggested. I tried every setting. But it just loses signal randomly. One minute it'll have perfect signal, the next it'll have none. Any suggestions?

Also, I have no trouble picking up wifi with the thing...