Skype for your smartphone, Skype is free, last I checked. Don't think Skype has a smartphone app though.
Just thought I'd take a look. They do. As long as your smartphone is Android or Blackberry.
http://www.skype.com/intl/en-us/get-skype/on-your-mobile/download/I'd consider getting a Skype account, but I have so many minutes on my plan that I don't use anyway... And enough rollover minutes that I could basically spend the whole month talking and still have minutes left... My kids only seem to use up minutes when I call them. Otherwise it's all text.