It's a little bit more problematic than you're thinking it is... I mean it's entirely possible, but it's not like "sure, somebody will have that out to you this afternoon!" Just use APG to encrypt messages and email them back and forth, possibly as attachments so you don't have to cut & paste I suppose. Not all that familiar with the app, but there has to be a PGP encryption app for iOS too. I have no clue what it is, but it's got to be out there.