Originally Posted by tsac
did you charge the battery? usually the radio will shut down at a low battery point.
Also SOS means no signal so the area may be having tower issues.
Thanks for the suggestions.
The first time this happened, the batter was somewhat low, but it happened again today on a very full (>90%) battery, and I have not had issues with it holding charge.
I get the SOS (along with the Invalid sim / initialization error) in my house and office, where I have pretty much 5 bars (when I actually get reception).