This feature may also be used to keep a UDP session open to a device that is located behind a network address translator (NAT). By sending the OPTIONS request, the UDP port binding in the NAT (on the outside address of the NAT/firewall device) is maintained by sending traffic through it. If the binding were to expire, there would be no way for Asterisk to initiate a call to the SIP device. This can be used in conjunction with the nat=yes setting.
CM Phone can now be registered in Asterisk GUI. I have registered CM Phone number succesfully in my IP01. The major difference of the registration between ATOM PC Server (APL) and IP01 GUI is that of missing outboundproxy, which is a MUST in GUI interface. At least, it is needed in my IP01.
Now, dialling out is of no problem. For dialling-in, guys please try by yourself and report here, would you. Thanks.