As of today, we have code that builds in AVR Studio 6 and provides basic (and only configurable at compile time) point-to-point serial-in, serial-out behavior. It packetizes incoming UART bytes and sends a packet only when there is a gap of 3 ms between characters or when a full 100 byte packet has been filled, whichever comes first.
I have a "command mode" partially built, so sending +++ with a 1 second pause before and after (and less than a 1 second pause between characters) will cause the state machine to switch to command mode and dump information about the current configuration. It then builds a command buffer (backspace is supported already) and when a carriage return or linefeed is received, it resets the command line buffer. Currently the command line is not parsed, but that's the next step.
Though the configuration (RF channel number, destination and source RF addresses) are configured at compile time, they are already stored in EEPROM and read out to RAM at power-up, so once the command parser works, updating the configuration will be quite easy.