you could install a voip application and buy a microphone to make calls over wifi and you can text message using email or aim. but you can only do it over wifi, you can't do it anywhere you want like an iphone can
well if could be only if:
1) you have open wifi networks covering a large portion
2) apple would allow microphones to be used with the Touch. The microphone input pin which is the same as the 5G iPod is active. However the Authentication Chip in the Touch will tell Dock Connector Microphones that it is incompatible with them and they therefore will not work.
3) there would be a good voip application like skype
4) it had bluetooth hardware
5) Steve jobs decided it was cheaper to just make the iPod Touch and iPhone(to drive production costs down) in the same factory and exactly the same but only ship different software on them.