With just 2 apps, you can completely turn your iPod to a iPhone with no monthly cost.
** This will ONLY work in a Wi-Fi area. this will not substitute a mobile cell-phone in anyway, so only expect it to be used at-home or at that computer-illiterate person's home who hasn't pass-protected their Wi-Fi. **
This is handy for replacing a home-phone or helping save on prepaid cell-phone minutes, though.
Or if you lose your phone. Which happens to me more then a lot.
Step 1: Calling - VoIP
App name: iCall free VoIP
Company: iCall inc.
Space required: 1.9mb
** NOTE: Only iPod 3G have built-in microphones. If you have a 1G or 2G iPod Touch, you have to buy a microphone that fits in the headphone jack. You can buy a nice one at RadioShack for only about $10 though. **
Other apps that work: TextPlus with Voice handy, becuase it also features texting.