Google Gmail now has a voice phone service. You can literally make calls from your PC to a phone that has a phone number (in other words, it's not a PC to PC service like Skype.)
The voice stuff is listed under "Chat" at the bottom on the left sidebar of the main page in Gmail.
In Windows, you install a small application that the browser launches for you when you select phone calls.
I just tried it. I called my office phone. The call went right through. The PC user uses the speakers and the microphone. The caller ID on the called phone says "Unknown Caller" with some arbitrary local phone number shown.
This was pretty easy, and it's free to call the US and Canada.