Not receiving SMS from Brightkite, but Brightkite's receiving SMS from me

I haven't been able to receive SMS from Brightkite all day (June 13). I don't get responses to check-ins or commands like "help". (All my updates today got assigned to the wrong location because I couldn't tell if check-ins succeeded!)

On the other hand, Brightkite appears to be receiving my SMS messages fine.

My phone service provider is T-Mobile To Go (prepaid plan). I know they've got a history of blocking shortcodes that annoy them, but I've never known them to let me send to a code that couldn't send to me.

My last SMS check-in before today was 06/09/09, so technically, the problem could have started before today and I just didn't notice.

An SMS gateway issue, maybe?