The IP address (to the outside world) that the iPod is at is actually the IP address of the cable modem (or DSL or whatever). So when you try to SSH into that IP, that request goes to cable modem and then the router, and the router doesn't know what to do with it. So on the router for whatever Internet connection the iPod Touch is using, you'll have to forward port 22 to the iPod Touch.
If you're using a neighbor's WiFi connection, you're pretty much out of luck, since you most likely won't be able to get into their router.
If you're using a neighbor's WiFi connection, you're pretty much out of luck, since you most likely won't be able to get into their router.