It's for all iPhones currently being used on T-Mobile. It's not just for the iPhone 5 to enable LTE. This will enable Visual Voicemail and set the correct APN settings.
Can't wait.
But does anyone know if this will break jailbreak? My understanding is that it shouldn't, correct?
I wouldn't think so, unless it actually comes as an update from apple. It should say a "carrier update is available" and not "a software update"