Sell your iPod Touch and use the cash you receive to buy an iPhone. Lol.
Or... use an app like Line2 to get a phone number that you can use for phone calls and text messaging. It will require wifi. If you have wifi at your house or frequent a place that offers wifi, great! If not, you could choose to buy a MiFi device and carry it around with you all the time so you could connect your iPod Touch to it anywhere. Of course, this is all at an additional cost.