Whatever happened to IM? Seriously, with data-plans and smart phones these days, do you even need SMS? I don't think Yahoo keeps a copy of every single IM sent between users, does it? Just set your client to not keep a history and bam, not electronic trail (and before you say the person on the other end could keep a history, why would they then agree to use TigerText if they want to black mail you anyway?).
Jeebus people, think things through before you do something you'll regret doing if you ever get caught doing it (or just don't do it, whatever).