[Zubersoft]

MobileSheets uses a TCP/IP connection to connect to other devices. If you use the "Direct Connect" option, you can specify any IP address you want in there. So what you'd have to do to connect to someone else on an entirely different network is specify the IP address used to connect their router or cable modem to the internet (you can find this by going to a site like https://whatismyipaddress.com/). On their end, they'd have to configure their router to allow these external connections, preferably just on the ports MobileSheets uses to connect. For the "Connect Tablets" feature, I use port 48000, so you'd need to allow that through the port forwarding in the router. 

I've never tested something like this before, so you'll have to let me know if it works.

Mike