If I'm reading this correctly, it appears to the serial port as a modem. Using PPP to another device, it would be essentially the same as using a dial-up modem to connect to the internet back in the day.
Said device could be something as simple as a WiFi router running OpenWRT, or, as Gorgonops suggested, any Unix/OS X computer on your network.
Now, if you wanted to get really fancy, you could drop an embedded wifi module that also runs some form of unix into the Duo or the Ultradock, and let that be your PPP-to-Internet bridge.