it would be cool to be able to reply to the text messages that people send to a 2-way device.... if there was a way to have the sender's address be "user@livejournal.com" instead of "livejournal@livejournal.com" (at least that's how it showed up on my end), then people with 2-way pagers can reply to the user's livejournal email address. obviously this would only work for paid users..
another idea... the ability to post new journal entries via 2-way devices. however, the only way of doing this is though email.. maybe there could be a way to accept journal entries via email, but only from a specified address.