Awesome project!

This would be fairly great fit for underwater UAV's, or like security camera way out on the edge of property. May be a good idea to post on ardu-sub related discussion forums. I'm not aware of an off the shelf module that's point to point ADSL, almost every modem is intended to yell at a ADSL / ADSL2+ host.

Did you run into any issues with consumer-grade gigabit switches negotiating 10Mbit?