3G and phone signal

Hello all, I installed the update for iphone last night. Normally I leave 3g switched of to save battery power. What seems to be happening now is that when I turn on 3g I loose my phone signal, which I may add was at full strength before turning on 3g. I reset the network settings, that didnt help. I called apple they told me to restore the phone. I have just restored the phone and still the problem persists. Do any of you people have the same problem, if so has anyone managed to resolve it.
Thank you

I notice that my signal does fluctuate when switching to and from 3G...

I'm now wondering if it needs the phone signal if it has a 3g signal. will it use the 3g signal instead of the phone.
Head scratching