Personally, I think USSD would be a better way to implement this. However, it seems the mobile carriers want to keep USSD to themselves. The 140 char limit in S

Personally, I think USSD would be a better way to implement this. However, it seems the mobile carriers want to keep USSD to themselves. The 140 char limit in SMS is a somewhat arbitrary limit in the GSM specs that we are no stuck with. Nevertheless, your solution (using id numbers) does seem quite clever but if this is going over a premium rate service then the SMS's will no longer be free.