This is strange, my experience with iphone 4 has been the opposite - reception more stable than my old 3G and works fine with Fiscon kit. The only slightly weird thing is that the contacts come up surname first whereas the 3G presented them the right way around. (3G used to play up since iOS3 installed a while ago)
I never had any stability problems with the reception - I just found the reception to be poor everywhere in comparison to my previous phones. I mainly use my phone for internet at work, but I get no internet signal at work!
Its a shame as it was a really nice phone to use and looked great. The Fiscon problems were minor and I could have easily lived with them... but I can't have a phone that has no internet!
Please note - I'm talking about my reception with NO HANDS on the phone

IF I held my fingers over the black bar in the left corner, I could get the signal to vanish!!
Perhaps its the area I work in doesn't have a very strong signal - but all previous phones have managed to get a decent signal.