hi, yes i have that issue with my 3G, too. its keep going blank after im done with the call, and its hard to end calls. the chance i guess is 50/50 for me. sometimes, it works fine, but sometime it just doesnt do anything. I'm going to apple store to find out the problem. It's not only me my buddy has that problem too. "HAVE YOU FIND A WAY TO SOLVE THIS ISSUE??"
an extra issue for me, loading up "contact" takes mad long, it takes too much time to load them up. basically its laggy pulling up softwares.
THX