I am trying to send DTMF tones to a certain extension. Here is the "set up" I have a 3CX PBX (has both SIP trunks and POtS trunks) which has regular extensions (i.e. SIP telephones), I also have ATA s(Grandstream 4004 & 4008) that pass telephone calls to POTS phones, including a ZetaFax Sever. The ZetaFax sever (two lines) listens, in band, for DTMF singaling as a way to route faxes to the appropriate end user. I am trying to see if there is a way to pass the "Called Number" SIP field via DTMF to the two ZetaFax "extensions"? Any ideas out there? I have looked at the setup fields for extenstions and see no setup option to allow this. I have already checked with several ATA manufactures to see if any support this without 3CX settings,but none apparently do. I tried the faxsever included with 3CX and needless to say T.38 is a dicey "standard" at best. Thanks.