If your computers are behind a 3G/4G mobile broadband router, you may be finding yourself without
a publicly accessible external IP address to call back to.
By default, most broadband plans would put you behind a private network which
means you cannot access your devices w/o being in the same network.
To solve this and get your provider to provide you with a public ip address, in
your 3G/4G routers, you should have an option to manually specify an APN.
Change them to the following:
M1: Good news! You don’t need to.