The Cult of Mac claims that the new iPod touch is VoIP-capable on the hardware side:
So who needs an AT&T-restricted iPhone? Course, you'll need to be in range of a Wi-Fi network to use VoIP on the iPod touch.With 5 wires connected to the Touch headphone jack (instead of 4 on the previous model), the device now supports the external microphone included with some headsets, according to Kyle Wiens of iFixit, who fully dismantled an iPod Touch on Wednesday.
It is worth pointing out that this is not the first time someone has run VoIP on the iPod touch. Touchmods added a microphone hack to the older iPod touch version. Another group enabled a SIP softphone client for the iPod touch to use with the "hacked-in" microphone.
With the new iPod touch - no hacking required.