onde:
We starting to investigate in RF field with something like this one https://www.sparkfun.com/products/10534What do you think about it?
That might work if you only need one-way communications and 4800 bps is fast enough. You will probably need something like an Arduino to translate from MAX to a wireless protocol (like VirtualWire). You will need the matching RF Link receiver on each receiving Arduino. If you are in the USA you should use the 315 MHz units instead of 434 MHz.