apparently it's being pushed now??
http://support.t-mobile.com/docs/DOC-5737
Notes:
T-Mobile Carrier Update
Version
Compatible with iOS software version 6.1.X
This update will not change the software version on your device.
Updated 4/05/2013
Available to all eligible iPhones using a T-Mobile SIM card
Features
Enables the following:
Visual Voicemail
4G network indicator
Commercial Mobile Alert 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)
Auto configures:
MMS Settings
Personal Hotspot Settings (Smartphone Mobile Hotspot)
APN settings for LTE connectivity
My Account bookmark
Improvements
Battery life (result of network/device optimization)
Prerequisites
T-Mobile iPhone or any officially unlocked GSM iPhone
Latest iOS software version
Device software is not jailbroken
50% battery life or connected to a power source
Data connection or a computer with iTunes and internet access
Minimum of 1 MB available memory (File size of update is ~10 KB)