This TinyShield is based around the Bluegiga BLE112 module and lets you connect your projects using Bluetooth 4 Low Energy (also known as Bluetooth Smart), which is supported on newer phones (like the iPhone 4s, and 5). This technology is great for low power sensors and accessories.

Includes power supply and level shifters on the board, so you can run your TinyDuino from 3.3V – 5V.

Tutorial here: TinyShield Bluetooth Low Energy