This problem has nothing to do with dialplan. Your Asterisk appears to be behind NAT and you have not configured it to know that. As a result when it responds to the Grandstream it provides a private IP address that the Grandstream can not contact.
You need to configure chan_sip to know it is behind NAT using the appropriate options in sip.conf
Yes, the IP telephone access the network behind a bridge of a laptop… otherwise is very strange because with one dialplan works properly, with another doesn’t work.