Yes, all servers are on the same administrative group and all AD fields are populated the same. That said, I have not asked users on different Exchange servers to try using the lookup feature as a comparison. It could be this one problem Exchange server.

I've been using my own account for testing. If I colleague who's mailbox resides on my Toronto Exchange looks me up, they will see all my contact information (home, work, fax, PIN and e-mail addy). If a user in our Montreal Exchange looks me up, they only see my fax and PIN.