If you're SIM is not connecting to a network, your device may be showing SOS Only or No Service, please try the following steps:
1. Turn your phone completely off, wait 15 seconds and then switch it back on (this solves many connection errors).
2. Try manually connecting to a network. To do this, go to your Settings and Network Settings in your handset and change network selection to Manual. Select a carrier and wait a few moments for the network to connect.
3. Try the SIM card in another phone (this will isolate if this is a handset issue or SIM card issue).