Some routers actually may not allow for Hushed calls to be either made or received. This is due to certain PORTS that we are using in order to deliver the VoIP call. Please make sure your router allows for the following ports to go through.
Required port for Hushed to function properly:
TCP: 10194 and 443
UDP: all ports between 10,000 and 60,000
There are good third party websites that will assist you with this task very effectively.