variant of the chip used in the Nokia Lumia 810 does not offer this feature.
This dovetails with a recent press release issued by the carrier in which the Nokia Lumia 810 was pointedly absent from a list of the carrier's 4G LTE devices. At this moment, T-Mobile offers two models with LTE connectivity, the Samsung GALAXY Note II and the BlackBerry Z10. On April 12th, a little ditty by the name of the Apple iPhone 5 will be added to the operator's LTE enabled lineup. A version of the Samsung Galaxy S III for T-Mobile carrying LTE support has already visited the FCC and should soon be made available.
As for the Nokia Lumia 810, it sucks to hear this guys, but it will not be updated to LTE.