What you require is just a desktop or a laptop with n internet connection and gmail ID, and you should be able to enjoy unlimited calls to your loved ones or business partners in US and Canada!
Chirp is supported on all major Windows platforms, it is easy to install and costs pennies a day for unlimited calls to the USA and Canada. A 3 day trial period of Chirp is available during promotional period to make Unlimited calls to the USA and Canada.
Please note that Chirp is not affiliated to Google and it's not responsible for google services.
I believe Google already allows you to make free calls to USA and Canada for free using the Goolge Voice Service.
Chirp one month license costs $1.49, 2 months at $2.99 and 6 months at $4.99.
What I would suggest you is to try Chirp for free with 3 days trial license. If you like the service and satisfied with it then you can purchase the paid license. The prices are too low for making unlimited calls.
For more info, visit Chirp.