No bars on iPhone but knows the network

Hi,

I have an iPhone 4S and its have connectivity issues.

The phone is always in a no-bar state. The network appears as _ _ _ _ _ Meteor 3G, but whenever a call is made it instantly drops and notifies me that the call has failed. Guys in shop said it might need a new antenna so I replaced it with one from a spare phone but it did nothing for the problem. I have cleaned the sim, tried other sims, hard resets, network resets, time fixes , antenna cable cleaning and restoring. Now the only thing that's given a result is restoring, after restore still before activation it has maybe 3/4 bars, but still not working if im called, and then i activate as normal, but after a minute or two it drops down to the no bar again.

This is very confusing for me and im really left stuck here. If you have any information or soloutins for this please tell me :)

thanks for reading.

Ken.