Devices supported on the GCI LTE network
Apple has released an update to iOS 6 that will enable iPhone 5 owners, on GCI, to connect to GCI’s blazingly fast LTE Network. The first step to getting connected is to update to iOS 6 and requires a GCI LTE Micro SIM.
On your iPhone 5, select Settings > General > Software Update and follow the instructions. For more details on the update, check out this support article.