I'm having the same problem and it is most definitely NOT a mis-configured email setting. It's also NOT an AT&T data outage. Here's how I know:
I just broke the glass on my original 8GB iPhone from June 2007 (it still hurts). So I go out and upgrade to the new 3G model. I get it up and running and everything is pretty well (just don't get me started on color temperature). Then I find the same +"endless connecting"+ issue with my email. Rebooting the phone does manage to get a connection and receive email, but that goes away in ten minutes or less. Holding down the Home key, ditto. If I write an email and try to send it out it just disappears entirely - no drafts folder, nothing in the Outbox or Sent folders. My iPhone accesses my 2 Gmail accounts, my Verizon account, my Comcast account, and 2 other pop accounts. None get past the "connecting" stage when this happens. None receive or can send email.
At the same time, I can jump on Safari and go to any web page I want. Stocks, weather, Maps, all have their connection. No hesitation, 3G speed does feel faster. All of this is the same whether on a WiFi or on 3G.
Now here's the thing - my original, first generation iPhone still works like a breeze. It's not active as a cell phone, but it's fully functional as an iPod Touch. On a WiFI it gets all my email, from all my addresses. I can send and receive, it can surf Safari and everything. It's been updated to v. 2.0.2, so it's running the same version of iPhone software as the 3G version. All the email that my 3G can't quite
connect to, my original iPhone is getting all the time. (And no, it's not removing it from the server so it's not there for my 3G, and some of my addresses are IMAP.)
So, you know, I'm just stumped. We
OBVIOUSLY need an update pronto.