Google Glass pulls data from the iPhone's cellular connection via Bluetooth tethering, but until now a number of Glass functions were limited.
The $1,500 Google Glass is currently limited to a select few users but is expected to ship next year at a significantly reduced price.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.
Article Link: Google Glass Will Soon Add Text and Navigation Support for iPhone Users