Very many routers (and yes, I'm talking about the kind you buy at Home Depot) out there have serial ports *inside* them (note J6 and J7 are both serial ports)....
http://devices.natetrue.com/musicap/12%20-%20Serial%20ports.jpg'>http://devices.natetrue.com/musicap/12%20-%20Serial%20ports.jpg
That's from (http://devices.natetrue.com/musicap/) a wireless music player built out of a router. It gives you an idea of the fun that can be had.
Here's alink to the OpenWRT hardware comapatibility guide which specifies the routers with serial ports...
http://wiki.openwrt.org/TableOfHardware?action=show&redirect=toh
It's not a plug and play solution, but potentially a very satisfying solution if you're into hacking around. I've thought about doing it with a wireless printserver/router that already gets used as a wireless bridge for ethernet enabled classic macs, but alas, it's not openwrt worthy.
Anyway, I know this isn't exactly what anyone wanted, and I didn't mean to hijack the thread, but I figured I should explain fully.