We saw a leak of OS 188.8.131.52 earlier which RIM has been pushing through carrier testing. I have been hearing conflicting opinions between OS 184.108.40.206 vs .205 about battery life but still its nice to see the GSM 9900 getting official OS love. Hopefully AT&T will jump on the bandwagon soon along with AT&T releases for the Torch lineup!
You can get the update by going to Options->Device->Software Updates to get the latest. My guess is it will also be available on T-Mobile’s download site shortly.