iPhone 4s always searching for network
Perhaps your Carrier Network Settings have been corrupted or altered in some way. In this case, the phone would be searching incorrectly for the carrier towers, or trying to connect and continually getting refused due to a setting error.

Apple provides details on checking and manually editing the settings, but getting them wrong can cause problems like you are experiencing. 

You can also restore your phone via iTunes, which will wipe the iPhone, reinstall iOS, and redownload the carrier settings. After confirming the restore worked, you can then restore from a backup to get your apps and settings back.