text messages beginning with '!' trigger automated responses?

Whenever I send a text message to my friend with an Android phone (further testing has shown this happens with iPhones as well, though not blackberries) that starts with '!', I get an automated response. I've detailed it in full , but to summarize: Me sending an SMS to my friend: "!test" results in me receiving an immediate response: "message test to XXXXXXXXXXX succeeded" and my friend receives: "test" XXX is where the destination phone number is. I find it concerning because I suspect it is the phone itself that is sending this automated reply, and for anyone who has to pay for outgoing text messages this could be an avenue for a third party to inflate their bill without them even knowing. Does anyone know what this is, why it's happening, or how to disable it?