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Not that this is a shocker, at this point, but David Murray, Associate Product Manager has announced IMAP capabilities as being available for all users this morning.
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IMAP functionality has a myriad of applications, and opens up the GMail platform for a number of uses it previously has been unable to fulfill, most notably iPhone synchronization. So long as you are using GMail with the US English interface, IMAP will appear in your inbox settings.
Google has also provided a helpful instructional video on how to further set it up for your iPhone, as well as Help Center articles to learn more about what IMAP can do for you.