The XBees (and Zigbee) support a bandwidth of around 56Kb/s. The XBess have A/D
converters so it may be possible to just use two XBees. Checkout "Making Things
Talk" from O'Reilly for some exmples.
I make a board with an '168 (Arduino bootloader) and an XBee on a single PCB.
The board can be cut into two usable halves. For more information checkout Loading...
(* jcl *)