Yesterday (my third day of Ting service) I received a text message saying "What's up" from a number I'd never heard of.
This one text put me in the S bracket. Because numbers are recycled, you end up getting random people who don't realize their friend changed phone numbers.
Ting currently provides 1MB of data per month for Android housekeeping. If you just made XS '1 minute, 1 text, 1 MB', that would go a long way towards solving this kind of problem. Telling someone on the phone 'wrong number' takes 1 minute as well. It also sounds a bit catchy.
Thanks and have a good day,