The 7920 is not officially supported on the 1250 platform. There are known issues with WPA(TKIP) interoperability. But I assume you are not using that otherwise would never even register. For not being able to make a call, does it say Network Busy? There was an issue a while back where the QBSS values were higher than they should be (CSCso63187). If the CU, which can also bee seen in the 7920 site survey is >= 105, then will get Network Busy. If you are hitting this, then would suggest to put the 7920 onto its own SSID and disable WMM as well as AP and Client CAC, where QBSS will not be sent to the phone. But then will not have the outbound CAC enabled either at that point.
Once you respond to the above providing more detailed info, we can go from there.
