Google Voice is one of the best ways to make a call over the internet. You can make free calls to an actual phone number, PC-to-PC calls, and free PC-to-phone calls.
Voice is much more than this, though. It's primarily a way to manage the phone numbers in your life and can intelligently route incoming Voice calls to any other phone you have or send them directly to voicemail. You can also screen calls and create custom away messages for specific contacts, and make groups within your contact list to apply rules to, like for custom call forwarding.
Other features include free SMS, free conference calls, and free voicemail services.
Free calls you make with Voice must be to numbers in the United States or Canada, and they're limited to three hours. However, you can continue to make a free call to the same number over and over again.
The Voice app works from the web as well as iPhone, iPad, and Android devices.