I have heard about this issue a few times today since BIS 2.5 went live with Windows Live push mail. So I thought it would be worth pointing out this Knowledgebase article that Remzi sent me.
Turns out that if you have Windows Live Messenger running on your computer it will not let your BlackBerry work with push Windows Live email. OBVIOUSLY this is by design.
Turns out that Microsoft built their email system protocol to only notify one client at a time and it communicates with the BIS and your computer as if they are two clients. Hence the conflict…
You can read about the problem here. RIM is recommending that you just install Windows Live Messenger on your BlackBerry and remove it from your desktop.
THE PROBLEM IS… that Windows Live Messenger is not available on all carriers!!!
Even the latest version that Josep sent me last week does not work on AT&T:
So what now RIM???