Almost the same problem here, same phone, OS, etc.
When connected to wifi the phone will sync with Exchange no problems. As soon as wifi is out of range or disabled the Outlook account won't even try to connect, indicating the typical 80072EFD or 80072EED errors.
No combination of data off, wifi off, reboots, etc, etc solves this. Come on Microsoft, this behavior only came with 7.5 and I see months of users reporting the same issue.
"Where are all the WM experts?"
Apparently busy with cosmetic updates that do little to restore functionality that existed in previous OS versions (heck, even the beta & dev previews worked better than RTM. ie: camera saved settings, exchange,
self-signed certificates, etc.).