It means you can only make emergency calls. There are two things you can try: Go to Manage Connections and try adjusting your mobile network settings from there (turning your radio off, then back on, might do it). And try a battery pull too.
Does anybody know what sos by antenna means i cant get any service?????????
As indicated by Sydneyk (thank you), SOS means you can only make emergency calls due to insuficient coverage.
In addition to the instructions provided by Sydneyk, go to menu, then options icon (the one that looks like a wrench), scroll down and select Mobile Network, and ensure you have 1XEV selected. Then simply power phone off and on.