I've currently been using the Google Sync capabilities of Gmail in the Iphone. I wanted to keep my contacts, calendars and Email in a central and safe place, and so far I've found that the Gmail servers do offer that possibility... So, why pay for MobileMe if you can have it for free? The Iphone setup won't take more than a few minutes, and not different of an exchange server setup.  Make sure you create a backup before syncing, and probably importing all contacts and calendars to Gmail will be the first good idea... :)

Follow the URL for further explanation and how to:  Setup your Iphone for Gmail Exchange capabilities