Last night I decided to restore my iphone4 to factory settings, as I have booked myself into an Apple store on Monday morning, and was preparing myself to possibly being given a replacement phone. Since restoring to factory settings, dare I say it, the phone seems to be working ok again. Now what I'm going to do next is gradually add contacts/music/applications.. and each time test the phone to see if the signal reduces... I'm wondering if its possible that there's an app that perhaps is always trying to connect to the internet and so is perhaps slowing down my connection, or even reducing my signal. Unlikely I know, but I'll give it a try and report back on here. But for now I'd suggest anyone thats having signal issues should try what I've done. Hope this helps.