Ok, I have been battling this for a while now and I am ready to rip my hair out. We are using the Audio Codes MP-114 FXO gateway ver. 5.0, the Polycom Sound Point 501 phones with SIP 2.2 and have just upgraded to the 3CX ver. 5 Enterprise Edition. Before upgrading we were having trouble with Double Talk, that is to say that when in conversation if the other party starts talking while I am still talking I don't hear them. It is as though we are on only half duplex instead of full. Now this only happens on external calls, internal calls work fine. We thought it was getting a little better and then we upgraded and now it seems worse. This is really annoying and poses a lot of problems in a business setting. Because it only happens during external calls I am sure that it something in the configuration of the gateway but I am at my wits end in trying to find where to correct it :? . Has anyone else had this problem and if so how did you correct it. For the record in 3CX the extensions are set to PBX delivers audio but not the gateway. I would appreciate any input on this.