Call North America phone from your Cellphone free

A lot of people know that Skype has ability to make a free call with North America until the end of 2006. I tried before, the voice quality is good enough.
But I am tied to my computer. The skype is only run on the computer.
Voxlib is a solution. 2013.08.29 Update: This site/service is down.

1) Install a skype and create a new account.
2) Download Voxlib client software, Vox for Skype, and Install it.
3) Setup your cellphone information in Voxlib.

Go to try it.

You can dial phone number within North America from your cellphone, through Skype and Vox.