Connection to gcs via mobile

Hey there folks…
I am in the final of building a navio drone for school, and I am now having a problem…
I do not have a full IP adress on my umts stick, so I will have to connect drone and gcs via VPN. I palnned to do this via hamachi, but they seem to have closed their free service. What are the alternatives? And how are you connecting yout drones via mobile network.
thanks for your answers!