Here is a facility to call USA or Canada Landline or Mobile Free of cost from your computer.

Oovoo is a free software which will allow you to call USA or Canada for free. All you have to do is download and install this application and create an account. This is a video chat software which is having too many features

Here are some

1. Video conversation and include up to six people

2. Send a video message

3. Recording video call

4. Text chat with up to six at a time

5. Send files

and many more

You can see the complete list of features here

Download it from here