Free PC to landine or cell phone software?

Do a search for Asterisk. You will find a fairly sophisticated, free Linux distribution with a robust user community

No, try this link for the download and portal to forums etc:

http://www.asterisk.org/

And this link for a start guide with links to related sites including a you tube video:

http://forums.digium.com/viewtopic.php?t=12319

And then there is a PBX project on SmallNetBuilder:

http://www.smallnetbuilder.com/content/view/24210/72/

For some reason the last link is goofey. If you type it in it works, but the hyperlink takes you to a page where you can find the article: How To: Building an Embedded Asterisk PBX.

Certainly an option, but asterisk will let you create a PBX as powerful or simple as you want.

No Asterisk is a tailored Linux distribution - which makes it a very powerful and allows it to run on minimal hardware (read cheap, old computers), but that also makes it a pain if you have absolutely zero interest in using Linux.

One other option is to buy a programable Analog Telephone Adapter, or ATA, like the Sipura SPA-3102 (I think Linksys bought them out). This will allow you to program a dialing plan to incorporate telephone features like selecting multiple VOIP service providers, call forwarding, conference calls, call screening etc.

The SPA-3102 is nice because you can insert it into your home telephone wiring and connect both to the telephone company and through your router or asterix computer (which is connected to the router). This gives you the option to use your broadband connection to make VOIP calls to save money, or the telephone company if you loose power, or your broadband connection stops working.