Fring lets you call from iPod Touch or iPhone over Skype

Fring Enables VoIP Calls Over Wi-Fi for iPhone with Skype Support – Mac Rumors

Can call directly using iPhone to another person with iPhone running Fring
– Call MSN or Skype users that are using their computer
– Call using Skype account, which allows you to have your own Skype number and at a discount rate for international calls
– Receive phone calls using Skype with your own custom Skype number
– Basic chat functions with most chat platforms, such as AIM, Yahoo and ICQ