Garmin has been a vocal champion of the ANT+ protocol, and today the company’s plans for an ANT+ adapter for Apple’s iPhone were revealed in FCC filings.  According to FCC documents, Garmin’s ANT+ iPhone adapter will work with the iPhone 3GS and iPhone 4 (no word on the iPhone 4S), and will attach to the bottom of the device, illustrated below.  We’re assuming that Garmin will also soon release an app for iOS devices which will allow the Garmin ANT+ adapter to receive data from various ANT+ sensors.

ANT+ sensors are often used in fitness equipment to wirelessly track data such as heartbeat, speed and temperature.  Garmin’s subsidiary, Dynastream Innovations, organized the ANT+ Alliance, and today the alliance has over 300 members, including Adidas, Microsoft, Sony Ericsson and TI.

Over time, we’d expect that Garmin’s ANT+ adapter will make the iPhone a more capable workout companion, while opening the doors for a number of other wireless applications.