TCP/IP to serial bridges already exist. I think that there are some standalone ones out there, but the book that I'm reading has a couple of examples for hobby projects. That includes both wired and wireless. Here's the one that they're talking about:

http://www.lantronix.com/device-networking/embedded-device-servers/xport.html

They appear to cost $50 or so.

It sounds like they look like a serial port to the hardware, so the wiring should be minimal and easy to figure out by anyone who understands pinouts. But I don't know how it encapsulates the data. I haven't reached that chapter yet.