那对call in有用，但对call out的意义何在？

If a call ia made to GV, it will be forwarded to SG, then SG will forward it to SS, then it calls the ATA. In this case, I see how the DIS SG provided works.


But if a call is made from ATA, it will accepted by SS, According to the OUT call plan,

sys.GoogleVoiceCall("username","password","14085551212","#{req.URI.User}","6265551212")

that call will be send to GV# 6265551212, and GV calls the finial dextination req.URI.User

In this case it seems to me that 14085551212 (SG #) will never be used during outgoing calls from the ATA. If is is not used, why do we need to specify it in the GoogleVoiceCall() call?