I have a user who is attempting to call a specific number in Nigeria (we are located in the United States). He has tried 4 calls, and I have now tried 3 calls. Every attempt fails: about half of the time the logs have SIP response code "606 Not Acceptable", and half of the time the logs have SIP response code "403 Forbidden". What could be going on here? We have made other calls to Nigeria successfully, but it's something about this particular number? Is it a codec issue? I tried with only GSM and G.722 enabled, and then again with all codecs enabled, and both failed. I'm not sure what else to try.