M.B.
You might want to consider the plan that vonage has:
http://www.vonage.com/features.php?feature=toll_free
It's only $4.99/month for up to 100 minutes, but does require you have a basic vonage plan, but those are available for as little as $14.99/month:
http://www.vonage.com/services.php?lid=nav_services
That's the phone service that we use for my kids' phone line - their phone is a "softclient" program that runs on their computer. You do need a headset/speaker as the ones typically built into computers don't provide good audio, but overall this is an extremely cost effective home phone. Here's the link to Vonage's softphone, which is only $9.99/month:
http://www.vonage.com/features.php?feature=softphone
I've been using this Voice over Internet Protocol for my main phone line for a several years and the quality has improved tremendously during that time.