Well, you could use a dual WAN router with 2 mobley's, though you would likely have to use another router for one of the connections because routers don't support two USB WANs (none that I know of but there may be some). Now, once you get past that hurdle (not difficult really), you won't get twice your speed. Your ISP has to support bonding, and so does your router, and we're talking lots of $$$ here. However, with load balancing, two users would be able to see 20 down each, but without bonding, the most any one user would see is 20. Also, if you run two speed tests simultaneously on the same machine, they may each show 20, meaning you are getting 40 total, but each session is only pulling 20.
Does that make sense?