You won't be able to get around using different URLs in terms of mail. But I doubt you're actually using Media Net instead of the WiFi. I just double-checked on mine, and when connected to WiFi and HSDPA (Media Net) all my traffic rolled across the WiFi connection. "Work" doesn't mean "No Internet," despite the fact that that's what it sounds like. You're probably just rolling out to the Internet side of the connection to get back in to the external URL.