I got it working today for my iPhone (actually I just set it up in Apple Mail and then synced the account to the iPhone).
It tags each message with an obnoxious "This message was sent via Synchronica Mobile Gateway." In addition to being annoying, I worry that someone at my company will see it and realize that I have given my username and password to a third party and that won't be looked upon with favor. So maybe no sending email from the iPhone at this point. Though that will suck.
I really just think of this as a stop-gap measure until Jobs & Co. come down from their ivory tower and license Exchange, but I'm not holding my breath.
I have no idea what to make of Jobs statement to USA Today that "they were working on it" in response to the question of corporate email and what those "pilot programs" are? Did he mean he was testing Exchange with big companies, or did he mean there were companies like Synchronica that were filling the void?
Edit: In the end I turned it off. It doesn't support SSL for either incoming or outgoing, which, I am not too worried about security (I don't email trade secrets) but it seems a little cavalier considering I use SSL for all my personal accounts. Plus, the annoying "This message was sent via Synchronica Mobile Gateway" stamp was really getting to me.