Hi,
In my case I'm connected back to Exchange Server 2007 using LTE on Verizon as the connection. I'm starting to think this issue has something to do with how the code on the iPhone interprets CDMA carriers??? Grasping at straws here cause I'm all out of options. I called Apple and they escalated my case to Engineering. Let's see what they come back with. I have users on iphone 5 with ATT and they report no problems whatsoever with push.
Just making sure that Apple hasn't started phasing out support for older versions of ActiveSync/Exchange.
A rough summary in the way Exchange ActiveSync works is this:
1. Mobile device initiates an ActiveSync connection to the mail server address using HTTP (usually over an SSL connection).
2. This device ID gets registered into the authenticated mailbox.
3. A keep-alive heartbeat happens between the device and Exchange every 120 second to keep push enabled.
4. As new email comes in, it hits a "trigger" on the mailbox to tell all registered & currently "alive" push devices to pull new email.
5. If the timeout expires due to 120 seconds lapsing, the device will need to re-register. Sometimes this is automatic , sometimes you have to force it (depending on the device).
6. The iPhone in particular requires a data connection through the cell network and will not use WiFi for push triggers (but will to pull the actual email). If there are any problems with the cell network, this can cause the heartbeat to go past 120 seconds and make the phone "push" keep-alive lapse.
So nothing specific to the way GSM/CDMA, as it is all just a web connection over the internet. However, buggy device software can cause issues. Mis-configured firewall rules in front of the Exchange server can cause issues. Data problems with the provider.
I did have an rare issue on my AT&T 4S where my cell data connection would just stop (this would kill my push email) and I would have to reboot to recover it.