The carrier update is available to all eligible iPhones using a T-Mobile SIM card.
Enables the following
● Visual Voicemail
● 4G network indicator
● Commercial Mobile Alter System (CMAS)
● AWS LTE (T-Mobile and officially unlocked AT&T iPhone 5 only)
● HD Voice (T-Mobile and officially unlocked AT&T iPhone 5 only)
● AWS HSPA+ (T-Mobile and new 2013 AT&T iPhone 5 only)
● MMS Settings
● Personal Hotspot Settings (Smartphone Mobile Hotspot)
● APN settings for LTE connectivity
● Battery life (result of network/device optimization)
You can update over the air (OTA) or via iTunes.