So why not keep on using gmail on the iPhone (via the IMAP interface)?
MM is nice for the push contacts/calendar, as well as multi-pc/mac syncing. Just continue to use gmail for mail, and use gmail's filters to autoforward all or select email messages to MM mail. That way, you only use MM mail as a "you have mail" alarm, handle all of your email via gmail, and don't have to deal with the sucky MM web interface.
If you want to go the cheap-*** route (and are feeling lucky), you can use the beta nuevasync for push google contacts/calendar, and the free yahoo mail for push iPhone mail (in place of MM mail for a "you have mail" alarm).
Either way, gmail FTW!