ExtUSB is an HTC proprietary connector that features a USB (with power) and Headset connections in a single combined connector. It is backwards-compatible with USB, but has extra 6 pins to support audio. The pinout is located here:
An updated version including support of video output on the Raphael can be found here:
Currently, the following HTC devices have this connector:
- Dream (The G1/Google/Android phone)
(* The Blackstone/Touch HD has no audio/headset on the ExtUSB, the sense pin seems connected, but triggers a 'not supported' message)
See Trinity_EMUConnector for more details on the signals provided in this connector, at least on the Trinity phone, if not all.