You can now get free outgoing calls to real phone numbers and free incoming calls to a real phone number. You may be thinking "who is crazy enough to be offering that kind of service free in both directions" and that would be a wise question. The truth is that no one company is doing that -- You need to be a little creative and combine services from two companies to get free calling in both directions.
Stanaphone has been offering a free phone number that allows you to receive free calls and free voice mail for quite some time. All you need to do is register and select the area code and they will assign you a free phone number. You can receive calls using their Windows based software or you can stay offline and just use them as free voice mail that gets forwarded to your email account.
Now Skype has started offering free outgoing calls to any US or Canadian phone number if you are in the US or Canada. You just need to download their free software (Windows, Mac, Linux) and register. You can then make all the free calls you want to regular phone numbers as well as to other Skype users. Skype will offer free outgoing calls until at least the end of 2006, and perhaps beyond.
Please note that some users may have trouble getting outgoing Skype calls to regular phone numbers to work. They check your IP address to make sure you are in the US or Canada, and there are some IP addresses that they wrongly identify as not being US or Canadian. They say they are working on that problem. Also note that the Skype software may indicate you need to purchase credits to make outgoing calls, but you can just ignore that message.
Either of these services alone is pretty cool, but combine them and you have one awesome freebie.