Let's start with a little geek speak: VOIP or voice over Internet Protocol is essentially the ability to make phone calls over the Internet.
With services like Skype, as long as both parties are on the Skype network, the call is free, but if you want to use Skype to call a regular land line or cell phone, it'll cost ya.
If you want the ability to make phone calls from your computer to any landline or cellphone in the US or Canada, look no further than Gmail!
Google combined the power of their Google Voice service into Gmail interface which makes it really simple to make a call.
Once you have the free plugin installed, just click on the phone icon in the left column and type in the any phone number in the US or Canada.
Or if you have the Gmail shortcuts enabled, just tap the letter "G" followed by the letter "P" to bring up the number dialer.
Or you can click on phone numbers in any email message and it will instantly bring up the dialer with that number!