Of all the iPod touch hacks out there this one is definitely worth keeping an eye on. According to MacNN, a developer known as Eok has created a semi-working VoIP client for the iPod touch using the SvSIP software for the Nintendo DS created by Samuel Vinson.
Although the iPod touch lacks a built-in microphone, a modder known as Marian managed to build a preamped mic for the iPod touch, meaning Apples portable media player could eventually be used as a handset to access VoIP services via Wi-Fi. At this stage, however, Eok has merely signaled calls in and out of the SIP server, but no audio (either incoming or outgoing) has been achieved yet. Still, it's progress.