Imagine having full on VoIP access not on your iPhone, but with your iPod Touch. Interesting, no? As it is really dumb in my book to bother with Skype on a device that already has a means of placing cheap phone calls without the app, Skype on an iPod Touch actually makes more sense to me personally.
I see being able to call on Skype as a really good thing, despite having to wait around for the nearest Wifi access point to make itself available. Clearly, this would be very helpful for those people out there who might not think to bother with a cell phone – like for overseas travelers perhaps?
As for the other VoIP solutions that will likely be available as well, I think there is plenty of room to share. The key will come down to functionality and comfort with what the end user is needing. But that is just my take.