I think you may be referring to GSP Tracker.
Deciding whether to get the touch or the phone goes way deeper than the GPS receiver. You have to realize that no matter how good Skype is the average cell phone buyer isn't going to want to drive around looking for open wifi hotspots to call home about dinner. Although a service like Skype would be a nice addition to the ipod touch it just isn't going be a deciding factor for the vast majority of buyers. (when deciding between the phone or touch)
Just about everyone I know owns a cell phone but I can't imagine even one of them give up their cell phone for a skype enabled device no matter how much it'll save them.
I agree- Prepaid cell phone (I like T-Mobile) + iPod Touch + Skype is the way to go. When you need to make a call you know will be long, you can wait for Wi-Fi and use Skype on the Touch, but you can still make those 1 minute calls back home.
However, I heard about a guy (yeah, yeah, I know) who was able to get a setup working where he had a SIM on a contract for unlimited data for only for $20 a month hooked up to something he built into his car (probably a cheap laptop). Whatever the SIM was in, he was able to utilize the cellular provider's internet with it and broadcast the connection though a Wi-FI network (yeah, in his car).
If you could wrap your head around that one, you just might have a dealbreaker for getting the Touch to use as a cell phone, because you could simply go to the Wi-Fi point in your car when you need to make a VoIP call on your iPod Touch.
Obviously that setup isn't practical for most people (not me! ), but for those who are willing to go through the trouble to save a few bucks, well... it sounds like an interesting possibility at the very least...