Iphone 3gs no service or network lost

[Escort]

Hello my name is Damir and I have iphone 3gs. Sorry for my bad English

"Modem firmware 06.15.00 and Version 4.3.3(8J2)"

I have iphone 3gs and signal go form 5 bar to 2 bar, 1 bar and no network. Then come NO SERVICE or just 1 bar (no network). My 3g is off because when is on 3g signal is 3 or 4 bars (it happens with 3g also), so 3g is off and display network lost after 1 hour network come back and have 5 bars all day, and every day display me network lost or NO SERVICE or searching... and after half an hour or 1 hour signal come back and stay 5 bars. when I go to carrier-> automatic is on... help please
I try
-reset network setings
-restet all setings
-reinstall Ultrasn0w
-look for antenna loose
-airplane off and on

I forgot to say that my iphone when signal come back he switch to another network (not my home network) and have full signal. When I turn off automatic and klick on my home network then message come "your selected cellular network is no longer available" and "searching..." and again take another network, and I go again to automatic, and again iphone don't take my home network, take another network and later I klick on home network and have a full signal till signal is lost again.

Modem firmware 06.15.00 and Version 4.3.3(8J2)

THX

[Escort]

nobody???
I notice when phone lose signal and start searching... or just stay NO SERVICE, I turn it off and wait for 5 minutes and when turn it on the signal come back and go to full bars and stay like that. iphone lose signal 3 times today and i turn off for 5 minutes and then turn on and signal come back every time :/
Forgot to say I restore my iPhone 3 days and not help...

[Escort]

Me again I have my signal back 7 days not losing signal when I don't use Wifi, when Wifi turn on and I'm on internet then start losing signal, then no service or searching...
anybody know why?