Make sure you make it easy to cancel, e.g. instructions in the first text for how to block your number from the registry. People who do not have a texting plan in favor of iMessage, Skype, etc. but do not block all incoming texts by default will thank you. I got a text like this recently from AIM mobile-something-or other from some weird spammy address. The second message contained instructions on how to block any future requests, but afaik I'm going to see all the messages that were sent in the meantime on my bill at $.10/ea– I'm glad I wasn't roaming, since the price essentially triples.