Our PSTN (Frontier Communications) provides 3 way calling & Call Transfer which require a "hookflash" in order to take advantage of the calling features. Currently I have a 3CX system with a Grandstream GXW4104 Analog FXO gateway and Yealink SIP-T38G phones. Currently when the 3CX system transfers a call to a mobile phone it consumes two of the POTS lines connected to the GXW4104 while the call is in progress. If I can get the system to do a blind transfer by initiating a hookflash, dialing the mobile number, and then hanging up, the call will transfer use the PSTNs transfer feature and the line will be free to take another call. This is much better than consuming 2 of our 3 available POTS lines. In addition, while on the phone, it is nice to be able to flash hook and then dial a second outside number to add another call to the line (3 way calling). Without the ability to send a manual flash hook to the PSTN it is impossible to take advantage of this feature. Any help would be greatly appreciated.