Holy crap, thank you Jon Mitchell, thank you very very much.
While it is somewhat well known that the best way to sync your Gmail account with Mac Mail and Google Calendars with iCal (especially if you have multiple calendars and want to be able to read, write, edit/have full functionality from your iPhone) is to set up Exchange, what seems to elude most users is how to send from your choice of email address.
While the Exchange server will fetch from multiple addresses, it won’t let you send from multiple. Sure, you could create multiple accounts in the iPhone’s settings, but that gets messy and has been known to clog up and cause problems.
The easiest/slickest solution? Fetch Calendars with Exchange, and fetch Gmail with ‘Other.’ Believe me, it’s true!
Read the wise, clear, and concise words of Mr. Mitchell at ReadWrite.com for how this works: