Hi, I am trying to transfer call to external GSM line from unregistered extension. The test was ONLY successful when I put 2 SIMs card in my VoiceBlue GSM Gateway. Otherwise with 1 SIM card, I always hear the error "Call transfer failed, Number Busy". But when I put the second SIM in the VBL it routes the call throught the second one and the two SIMS are engagged which is not good enough because I want the two SIMS to be freed once the transfer is completed. Let me explain step by step: 1. I called the VBL GSM Gateway through SIM 1 number. 2. The DR welcomes bla bla bla and I pressed 5 on my phone. 3. Digit 5 is connected to an unregistered EXT that perpetually make an external line to my second phone number 4. With the 2nd SIM in the VBL gateway, I got the call on my second phone. OK 5. With ONLY one SIM in the VBL, i heard an error annoucement "Call transfer failed, Number Busy". I prefer to use only only one SIM to complete the transfer. I also can afford to have the second SIM in the VBL if and only if, the two SIMs will be freed after i picked the call on my second phone, so that the two SIMs can leave me alone with my phones to talk and be ready to attend to another call. Hope this is clear. Br, Ben O.