As noted by Kevin Werbach and others, Jeff Pulver, the originator of FreeWorldDialup, the Pulver Innovations WiSIP phone, and a host of other telco-tweaking apps, is at it again. He's launched Bellster, which allows its participants more-or-less no-extra-charge phone calls worldwide. "No extra charge" is significant because it's not free -- in order for the service to work, each participant has to have some sort of reasonably bulk usage plan in their local calling area/country.
My take? RIght now, the short answer is, it's a stunt. A cool stunt that is interesting and will cause big telcos more worries than actual revenue problems. Like BitTorrent, its gnarly technical requirements will keep it from touching more than 1% of the userbase. Basically, you have to set up a dedicated Linux Asterix PBX server in your house to share your phone line with others. Not something that the average user is going to do.
Now... when someone rewrites Asterix into a PC application that runs on Windows, with a slick user interface a la Skype, and adds Bellster functionality, and says to every dummy (cough) user in the world, "Plug your phone line into your PC, download our app, and you get free phone calls worldwide" ... then, the telcos have a problem.