It may be a day late, but we’ll take it. The T-Mobile HTC 8X is receiving the Portico update as we speak. Yesterday it got delayed, but thankfully the delay only lasted one day. According to T-Mobile support forums the update started at 1PM ET. The Portico update addresses a number of issues and adds some new functionality. The two major things are a fix for the random reboots and SMS call reject. You can see an in-depth look at what Portico has to offer here.
To check for the update go to Settings>Phone Update>Check for Updates. Downloading and installing should take around 30 minutes. Cheers!