I hope they do announce devices. One of the big issues with T-Mobile right now is a lack of LTE devices, particularly mid to low level devices. At this point, your choice for an LTE device is the Samsung S4, the new S3 (but most users have the old S3 without LTE), Note 2, HTC One, iPhone 5, and Blackberry Q10 and Z10. Additionally the Nokia Lumia 925 is being released on the 17th, and it appears they have just announced the Sony Xperia Z.
I would say that LTE is worthless for most current T-Mobile customers, at the moment, since it would require them buying a new $600+ phone (since most are still on contracts they signed prior to March).