How about Keychain syncing for the iPhone? If it's already there, how about making it work right?
Also, it's definitely worth looking into copying RIM's unified Messages app. Basically it collects together all incoming SMS, e-mail, IM, etc. Make it accessible to third party apps also.
I think I've mentioned this before but it's worth repeating; let me use the iPhone as a remote speaker.
Thank you in advance,