Ah, forgive me, I had thought you had already put it in the BWC. My option was for if it didn't accept the nextel mail for some reason...
Of course, the easiest way to change this is to go here:
http://www.nextel.com/en/solutions/b..._service.shtml
click "Access the BlackBerry® Internet Email Service now! » "
Log in, go to profile, select other email accounts, select add account, enter in the info, click submit, if it asks for more information, *then* type in the mailserver...