[thisisparker]

For Android, see the Guardian Project's work, especially Gibberbot: https://guardianproject.info/apps/gibber/

For iOS, you could try ChatSecure: http://chrisballinger.info/apps/chatsecure/

If you want to use the same key on both clients (which carries some additional risks if, say, your phone gets stolen, given that key is stored in plaintext) you may find the Guardian Project's documentation of different OTR key file formats useful: https://github.com/guardianproject/otrfileconverter

[marcog1]

Thanks! I'll take a look at Gibberbot.

[XorNot]

There's also Xabber which has OTR support (and can speak MSN, which is very helpful).