The ! command is set in settings - settings -Transfer/Record, you need to identify the correct DTMF tones of your PBX or Voice Modem that allows a call transfer or the transfer will fail. AFAIK IVM tells the PBX hardware to do the transfer on its behalf, so if your PBX can do a transfer succesfully it allows IVM to do a transfer successfully. Just a note on the PBX I am experimenting with ! means disconnect/hangup not hook as stated in the manual.