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In a conversation with a Google employee who is working on the Glass project, Frederic Lardinois was informed that they are adding more-complete iPhone compatibility to Glass “very soon”:

 Glass, the Google employee told me, will soon be able to handle these features independent of the device the user has paired it to (and maybe even independent of the Glass companion app).

While Glass will happily work with any iPhone over Bluetooth or use any Wi-Fi connection to get online, iPhone users are currently unable to get turn-by-turn directions through Glass – one of its killer features. Those direction are pretty useful while you are navigating a new city and they do show off the power of location-based apps on Glass, but the software will currently balk if you ask it to give you directions while it’s connected to an iPhone.

For Android phone users, Glass owners have to run a companion app on their connected phone to enable all of Glass’ functionality. However, it is unclear how complete feature parity is going to be achieved on the more-restricted iOS.

In regard to navigation, the Glass unit needs the tethered phone to act as a proxy for the GPS, as turn-by-turn navigation requires highly-accurate location data. On iOS, this is possible but a companion app will be necessary.  From a technical perspective, Google’s companion app can use the CoreBluetooth framework, introduced in iOS 5, to interact with the Glass. When a user asks for navigation on the Glass, the device sends a message to the phone app to actually perform the heavy lifting.

For SMS, Glass can intercept text messages notifications in the same way the Pebble watch does, using the Bluetooth MAP profile. However, replying to messages is currently inconceivable with current iOS security policies. On iOS, the only way for developers to send SMS’ (or iMessages) is to present an Apple-controlled view with a pre-filled message. The actual sending of the text must be controlled by user action and cannot be achieved programatically, unlike Android where any app can send SMS’ on a user’s behalf as long as the user agrees to allow the app to have the appropriate permission.

Therefore, whilst a companion iOS app for Glass will open up more of the features that Android phone owners currently enjoy, until Apple loosens the security policies on iOS (or makes an exception for Google, which is extremely unlikely to happen), it can never reach true feature parity for iPhone users.