Apple's External Accessory framework

Apple came up with an fantastic accessory framework for other devices or gadgets to work with Iphone, Ipod and IPad. This particular program is known as MFI (Made For Iphone, Made For Ipad, Made For Ipod). The Made for iPod, Made for iPhone, and Made for iPad logos mean that an electronic accessory has been designed to connect specifically to iPod, iPhone, or iPad and has been certified by the developer to meet Apple performance standards.Developers receive technical specifications describing the iPod Accessory protocol, the communication protocol used to interact with iPod, iPhone, and iPad. Developers also gain access to the hardware connectors and components that are required to manufacture iPod, iPhone, and iPad accessories.

For more info refer link  http://developer.apple.com/programs/mfi/


For Using External Accessory Framework with Bluetooth devices refer the following link
http://developer.apple.com/library/ios/#qa/qa2009/qa1657.html