Recently I have dived into VoIP (Voice over Internet Protocol) which can use a simple analogue phone to make phone calls using broadband in lieu of a PSTN account.
VoIP has been around for several years, but I had always been a bit dubious of the claims made by providers (MagicJack and others).
I went the way of buying an ATA (Analogue Telephone Adapter) which connects your analogue handset to your network router. I actually bought two ATA devices so I could run various tests. They were both Obihai devices, one an OBI100 ($40) 
and the other an OBI110 ($50) and both bought from Amazon.com. See www.obihai.com for more on these devices.
Free Calls:
I was not planning on using a free call VoIP provider, but ended up trying the Google Voice as a SIP connection. This will give free calls to USA/Canadian numbers until at least December 31 2012. Google may decide to extend that date or otherwise may start charging a per minute rate. The setting up of the ATA and Phone to use Google voice account was a multistep process and will be discussed further below.
Paid For Calls:
There are many options for adding paid for calls, from monthly subscriptions that will give you x minutes of free included calls each month, to some that simply charge you for the calls made. For my second OBI device, I chose a mix of the two. I subscribed to a DID (Direct Inward Dialing) phone number at a cost of $0.99c per month, and calls that will cost between $0.01 and $0.02 per minute. For this, I chose to use VOIP.ms
Call Quality:
Testing incoming and outgoing calls with both connections (VoIP.ms and GoogleVoice) has been very good. In one test using the GV line, a call between USA and Australia was better than an expensive $2.00 per minute PSTN call I have made. This one cost just $0.02 per minute.
Setting Up Google Voice Line:
There are some requirements here. First you need a Gmail account and then sign up for a Google Voice account.
You also need a broadband internet connection and a free account with Obitalk.com which you use to do some connection configuration. Be prepared to enter your gmail account and gmail password for this to work. If you are a little apprehensive to do this, set up a separate Gmail account and GVoice using that separate gmail account.
Rather than me explain all the processes, have a look at the guides provided over at the ObiTalk web site.
You will be up and running in minutes once you have your Obi device.
Setting Up VoIP.ms Line:
To use the VoIP.ms system for only outward calls, you do not need the DID (Direct Inward Dialing) number. The process of getting the Phone and Obi ATA device connected was simple and is explained in detail at the Voip.ms wiki webpages.
Other Devices:
I read a recent review where there was some praise for the latest version of “MagicJack Plus”. This is basically another ATA device but it is locked to the MagicJack SIP provider. There is an annual fee to join MagicJack and it can be economical if you make lots of calls. I have not tested with MJ so leave that up to you to play with if you feel it would suit your situation.
Overall, I am impressed with the latest VoIP devices and SIP providers. If you get the urge, give it a try out.
John