VOIP? Whats that? sorry never heard.

Brain? Cable? Computer?

VOIP is an acronym for Voice Over Internet Protocol. It is like making a phone call, but it is done over the internet which can make it either rather cheap, or free, depending on both ends. You could replace your normal phone line with it if you wanted to, but then you are dependant on power during emergencies, and you have to make sure the emergency numbers know where the phone is in case they need to get their services to reach you.

So the basic requirements are quite simple:
Broadband
And VOIP system

By the system, it could be a few things. The simplist might be to just download a program like Skype off the internet for free, and make phone calls using it to other people. If they have Skype, then calls are free, otherwise you can make cheap calls using it by prepaying Skype. I haven't bothered to do any of this. This might not even require broadband, and dial up might work, but the quality would be lower that way. I remember hearing in a review somewhere that the quality has varied.
You can also go down to your tech store and ask about a Skype phone, or some other VOIP phone. You can get it and then plug it into your broadband router, and the product/retailer should instruct you about how to get it all set up.