I don't think it's limited to Verizon BIS. I'm on Sprint and I'm getting an error that my browser is unsupported and I need to use either MediaNet or the BlackBerry Browser. I am using the BlackBerry Browser.
It's not a generic 50 whatever or 403 error though...it's an NBC created OOPS! page.
Posted from my CrackBerry at wapforums.crackberry.com