Here's an odd one. I set up an extension to serve as a relay to our IVR for inbound direct SIP calls (not thru a provider) to our 3CX. I have several extensions already answering direct-in SIP calls successfully. The SIP addresses for these are email@example.com, where sipid is the SIP ID as set on the extension's Other tab, for example sip:firstname.lastname@example.org for an extension where the SIP ID is 'bozo'. Note: it is an old wives' tale that the SIP ID must be set to the extension number. So I thought, this'll be easy. It wasn't. All I got was the famous unrecognized call error. For grins I changed the SIP ID to = the extension number and it worked! But I have 4 other extensions that have "real" SIP IDs and they work! It turned out that the cause of the errors was the Outbound Caller ID, which I had set to an alpha string instead of a number. Why I don't know since that extension will never place an outboun d call... but I did. After experimenting with the Outbound Caller ID I found that you can put just about anything in it except a hyphen (and probably other punctuation). My original Outbound Caller ID had a '-' in it. I'm reporting this because it may be the cause of some of the assertions about the SIP ID needing to be equal to the extension number, and because it seems like a bug that the Outbound Caller ID contents affects the success of direct inbound SIP calls to the extensions SIP ID.