I also used to use the Motorola Corporate Directory. While the new Froyo features give you GAL for email addresses, they do not give you GAL for phone numbers.
dblhelix -- have you tried Touchdown? Even if you don't want to use it for all of your Exchange integration, you could use it for phone number lookup.
Personally, I now use Touchdown. Under the latest Froyo, my company's rules forced me to enter a password everytime my screen dimmed. That drove me nuts. Touchdown only makes me enter a password the first time I use Touchdown after a boot.