According to All Acronyms, "SOS" has the primary meaning of "same old stuff" when used in a text message. This acronym can also mean "someone over shoulder," "someone special" and "save our souls."
"SOS" and other acronyms like it are all part of SMS language, or textese. This simplified language uses abbreviations and acronyms to facilitate faster typing, getting the meaning across while conserving space and time when texting, emailing or instant messaging on the Internet. Other commonly used acronyms include LOL (laughing out loud), TXH (thanks), B4 (before), C U (see you), ATM (at the moment) and ASAP (as soon as possible).