That's right, until T-Mobile issues an update to support SDIO, SD WiFi cards won't work. I've been told they're working on an SD camera, which also requires SDIO, so I'm hoping they'll extend support to all SDIO devices including network cards. I've never gotten a firm answer on that though.
All Pocket PC 2002 come with the generic network drivers you mentioned. Their presence, unfortuately, doesn't mean that there's hardware out there for you to buy for the T-Mobile.
-------------------- Lisa Gade Editor in Chief, MobileTechReview