I was also experiencing the exact same issue, where i would have a decent signal when the phone was lying flat and then it would drop upon picking it up. If it was somewhere with an already weak 2g signal, then sometimes it would drop out altogether - then i wouldnt come back until i restarted the phone.
However for some truely bizarre reason, removing the plastic back cover seems to fix this for me... this is obviously not ideal, but i have a silicon case also - so the battery, sim etc ate still covered/protected.
Can some of you guys try this and tell me if you have the same outcome...?
Edited by rosco-85, 10 June 2012 - 11:09 PM.