I'm having the exact same problems with my S2 only I don't get emails or cannot connect to the internet for weeks at a time.
I'm with Bell Mobility.
I have a Samsung Galaxy S2 on AT&T. From the first day I got the phone (about 2 months ago) I get an error (on occassion) that says "unable to connect to server". When this occurs my email won't work and I can not access the internet. This doesn't happen all the time, but at least once per day and it can last 2+ days. Then all of a sudden it works again. Sometimes I turn the phone off and back on again. That fixes the problem only 1/2 the time, but even in those cases the problem comes back again consistently.