Looking at the Arduino Servo shield, it can be seen that there is an APC220 connector.
The APC220 radio module provides a simple and economic solution to wireless data communications. It integrates an embedded high speed microprocessor and high performance IC that creates a transparent UART/TTL interface, and eliminates any need for packetising and data encoding.
In short, it is a great little, low cost, module, with a good range, which enables you to easily build wireless projects.
- Transmit distance up to 1000 m (line of sight) @ 9600 bps
- 256 bytes data buffer
- High sensitivity (-112 dBm @ 9600 bps)
- GFSK modulation
- UART/TTL interface
- Embedded watch dog
- Size: 37 x 17 x 6.5 mm (1.46 x 0.67 x 0.26 in)
On ebay, APC220 Wireless Communication Module for Arduino+USB Converter, the pair go for about £20.