http://ipodtouchtricks.net/iPod-touch-tricks/voip-support-on-ipod-touch-2g-confirmed/
according to this site i guess you can
You first have to download a torrent of the version of firmware you want, and then you can install it onto your iPod touch
You have to know the password and the email
Yes, using RingCental your ipod touch mobile can be VoIP SIP phone. You only need to connect to internet and use ringcentral soft phone to make voip calls.
Yes, Some VoIP services are applicable to PSP.
There is no such thing as 'installing' an iPod Touch.
no because the ipod touch 4 is a newer version
You can install the Bump app that is made for the iPhone and iPod Touch. There isn't an iPad version yet.
If you can't access apps on the iPod Touch, then you should try updating the software version of your iPod Touch to the latest version.
there are a few voip apps that can be used to make calls
no
You can install free text messaging apps, but you have to pay for minutes to call people on the iPod Touch.
Assuming you have at least a 2nd generation iPod Touch (1st generation iPod Touches do not support iOS 4.) simply plug your iPod Touch into your computer and open iTunes. You will be automatically prompted to update your iPod Touch. If not, find your iPod on the left hand side. Click your iPod and your iPod's information will open. Click the button labelled "Check for updates" and your iPod Touch will be automatically updated to the latest iOS version.