Hi, i've read that phones 7920 are not officially supported by AIR-LAP1252. But, are they supported when you work with autonomus 1252?
Just to add a doc to the great tips from Michael (+5 points here Michael :)
Cisco Unified Wireless IP Phone 7920 Version 3.0
Cisco Aironet access points, including the Cisco Aironet 1300, Aironet 1200, Aironet 1100, Aironet 350, and Aironet 340 series, the Cisco Aironet 1100 Series Lightweight, and the Cisco Aironet 1130
Hope this helps!