We have a guy who has a Sprint Sierra Wireless 250U USB 3G/4G aircard. He can connect through 3G just fine. He connects to VPN and everything works fine.
When he switches his aircard to 4G to take advantage of the faster internet speeds, he then connects to the VPN, then all works fine but his Outlook will not connect through to the our exchange server.
Environment: Windows XP, Exchange 2003, Outlook 2007, Open VPN