[stanforder]

I have it on good authority that this will work soon / should work now for most people. Two points:

1) Be sure to have calendar enabled on your domain. (Go to "Manage domain" and enable it.)

2) For a small number of domains it doesn't work even if calendar is enabled. That's a bug in the registration server and it should be fixed by tomorrow (Wednesday).

And a bonus remark:

(3) You can use only one Google account, so you can't switch between your domain and a regular gmail account.

Disclaimer: I don't work for Android but I'm pretty certain the info above is more correct than what T-Mobile told you.