BES is carrier independant. BES has NOTHING to do with the specific carriers. Here's the basic link:

BB (Phone) talk to carrier (Sprint/Verizon/whatever). Carrier has links to RIM. RIM has a link to the specific BES through a secure link. BES talks to your e-mail server (Exchange, Domino, Groupwise), which talk to your e-mail client (Outlook, for example).

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The link from BES is to RIM, not to the carrier.

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