The new 2G iPod has 5 wires connected to the headphone jack (instead of 4 on the previous model) meaning that the device now supports the external microphone included with some headsets. This information comes from Kyle Wiens of iFixit, who fully disassembled an iPod Touch on Wednesday.
Im very excited about the possibility of VOIP on [the Touch],said Wiens. Now we just need the software.
Apple has said it would not permit applications that run VoIP using cellular networks; however, a wi-fi only version would definitely be a possibility for new iPod which has no cellular access.
Via Cult of Mac