Hello guys, thanks for your replies. I am glad to see the discussion! Morgan, if you could post the configuration steps or send them in an email (email@example.com), that will help a lot!
FYI, I have not been able to get the Avaya IP phones to directly “register” with Cisco Call Manager OR get the Avaya IP phone to work as H.323 client. Here’s what works for me:
1) You can configure a H.323 IP Trunk between an existing CM cluster and Avaya S8300 (or S8700 for that matter) and get calls working in both directions.
2) Ditto for supplementary services.