You need to have DSL or Cable internet. You plug it in any USB druve then plug a landline phone, and you can use it like a landline phone, but it cost like 10 bucks per month. goto magicjack.com and find more info.
Actually it only costs about $29.00 per YEAR. I had it several years, then it quit working, they sent me a new one but I couldn't get it to work right, something with my usb port. I gave up. I have a new computer now and need to get mine going again. It was great while I had it.