If I understand it correctly, you want to use RFtoy to make a transmitter (motion sensor) and have OSPi as a receiver, is that right? Since RFtoy itself is an Arduino, you can program it to read the motion sensor, and send the value out through RF transmitter. On the OSPi side, you can modify the firmware accordingly to read data from the receiver and trigger actions (like turning on a sprinkler program or something). OSPi has pinouts to fit a RF transmitter (the purpose is to allow OSPi to talk to RF power sockets), but there is no reason you can’t use the same pinout to connect a receiver instead (both transmitter and receiver require 3 pins: VIN (+5V), GND, and data). Of course you can also use any of the other available pins for receiver.