I have a very strange problem with my Samsung Galaxy S II. When I have a WiFi connection I'm able to sync all of my mail accounts, Yahoo, Google, & Exchange. When I'm connected to the mobile data network (AT&T) I can sync Yahoo & Google but not Exchange. I have no problem connecting to our exchange server via webmail through my browser while connected on the mobile data network. In my office, I turned WiFi off, opened email and and clicked refresh. My WiFi turned itself back on and connected to exchange. I disconnected from our WiFi network, turned WiFi off again and I got the message WiFi networks are available. If I'm out side of the office where there is no WiFi connection, I get the message unable to connect. I can change to one of my other mail account click refresh and my mail from those servers will download. I've gone through all of the mail setting for my exchange account on the phone and I'm not seeing anything that would restrict it from connecting to my exchange server via mobile data.