Update: this press release completes the story, the 8525 is no longer the "Cingular 8525" but the "AT&T 8525 Pocket PC." The rebranded version already has the ROM update mentioned below pre-installed. Now we just have to wait for WM6 for it. Sadly, I'm betting it won't come anytime before the already-feel-like-an-eternal-wait update for the Blackjack. In other words, I'm betting on the fall.
Over at HTC's support page for the Cingular/AT&T 8525 you'll find a ROM update for your slider. It adds Push-to-Talk, support for Cingy's video service, and a bit more. Seems odd that they're even bothering given the fact that they've also promised a Windows Mobile 6 update sometime in the near future. Oh well, the folks over at HTC had to have put some work into the update, you may as well reward them by installing it.
Remember: ROM updates wipe everything you have on the phone. They also, if done haphazardly, can brick it. Proceed with deliberation and caution, as always.