The curious collection of a slightly mad scientist
It seems AT&T has to have your iPhone on the Microsoft Push (aka Enterprise Data) plan.
If you purchased an Unlimited data plan and your iPhone stops working, check that they didn’t slyly switch you to a different smaller data plan. You should be grandfathered in… at the same price. I may have to still argue with them about that. I think mine was $30 for unlimited, a few years ago.
Your Exchange Server may be set up correctly and others may be having now problems. You may be able to set up your account, and that works. After entering your Exchange server information on your iPhone, you see “Configuring Sync” and no error, but still … you get the “Cannot Get Mail – The connection to the server failed” message.
You should now get email and your calendar items from your Exchange server. I have not seen this fix on the net, but this is what worked for me today.
Here are some links for your Exchange Server Admin if everyone is having problems:
Hints for Exchange server admins: Check the logs to see if your mobile users are getting in: (Default is C:\WINDOWS\system32\LogFiles\W3SVC1). In my case, my iPhone was showing up in the Exchange Server logs as making requests, and Exchange server was set up correctly, but I still could not get email due to my AT&T data plan!
I hope this saves someone hours, days, or even weeks of frustration and work.