WigdaddyUSB On-The-Go, often abbreviated to USB OTG or just OTG, is a specification first used in late 2001 that allows USB devices, such as tablets or smartphones, to act as a host, allowing other USB devices, such as USB flash drives, digital cameras, mice or keyboards, to be attached to them. Use of USB OTG allows those devices to switch back and forth between the roles of host and device. For instance, a mobile phone may read from removable media as the host device, but present itself as a USB Mass Storage Device when connected to a host computer.In other words, USB OTG introduces the concept of a device performing both master and slave roles – whenever two USB devices are connected and one of them is a USB OTG device, they establish a communication link. The device controlling the link is called the master or host, while the other is called the slave or peripheral.
I just read the news somewhere, the beta version of iOS not support it, but this is not the final version.