phone will show reception then lose reception rendering it useless
I have an iphone 3gs approx. 8 months old. One day out of the blue it had no reception. Couldn't make a call nor receive one, couldn't send or receive texts either. Tried a couple of manual resets with no luck. The phone would however start randomly getting reception for short periods of time and then go back to nothing. I have had it sitting in a drawer at work for about a month or so and my wife damaged her phone so I thought I'd give it another try. I reset the phone back to factory settings, added her sim and restored from her last backup. Viola, everything pulled up great and phone was working perfect. It's been about 3 hours and now it is back doing what it was doing before. Any ideas what to look for? I really need to get the phone working to avoid buying another to replace my wifes. Thanks!
Most likely your antenna inside the iPhone is loose from the motherboard. This connector tends to get loose quite often.
Best is to open your iPhone and check and reseat the antenna connector in the bottom right of the phone (nr. 7)
If that does not solve it you may want to replace the antenna:
Replace a damaged docking port — 47 available at 49.95 each.