I cannot answer your specific question, but I cannot see how Mobile Me would be workable without a computer in the chain. Don't you sync your iPhone on a computer somewhere/sometime?
BTW, I meant to say that Mobile Me is pretty cool and I don't even have an iPhone. All of our family calendars, contacts, email, etc, is right there, and I use the photo gallery to upload and host pics all the time. Good stuff, and much improved from the former Dot Mac version.