I have a UC520 and it runs SIP to the ISP. Outgoing calls works fine but not incoming. The configuration is posted in a .txt file. Anyone that has any suggestions to what it could be?
Means mismatched codec, see the ITSP doesn't use G.711 that is cisco default. Just put "codec G.711" under the incoming voip DP.
Hope this helps, please rate post if it does!