iPhone 4s, has been losing the network

My iPhone 4, 5.0.1 firmware regularly loses network, and does not catch it again.On the phone constantly, "No Network". Displays the message "Error SIM-card" if it is not used for a long time.

Restore the work is only possible with a full reset iPhone. On firmware 5.0.0 had no problems. Phone never fell into the water and did not get. What to do. No action torestore and reset do not help.

Use the phone in Russian, was bought in Germany. GSM, the operator Beeline,replaced the SIM card to the new.

And the phone is constantly buggy.