By default and for security reasons, E Street restricts access to our voice platform (E Street Voice Pilot https://www.estreet.com/voice) to US based IP addresses. As a result, using Communicator or Communicator Go from a non-US country may fail.
The solution is to use a VPN. A VPN will tunnel your VoIP traffic as if it is on an Internet connection based in the US. This will allow Communicator to work from your PC, and Communicator Go to work from your Smartphone.
These VPN companies are known to work well with VoIP:
You would just install that VPN on your mobile device, then connect to any US based VPN site (some of them even have a Denver, CO USA locations). Once connected, start your Communicator Go app on your mobile device and/or Communicator softphone on your computer, and you should be able to make and receive calls like normal.
By doing this it makes you look like you are connecting from the United States. PLUS, it encrypts all of your Internet traffic adding an extra layer of security and certainty.