User will click to talk to the advertiser via the Skype technology recently bought by ebay rather than just going to the advertisers site. It says advertisers are willing to pay up to 10 times more than a click through i.e. adsense. Here is the source: http://www.nytimes.com/2006/08/29/technology/29ebay.html?ref=business
I think initially those ads will only be on googles search pages, but eventually they may be put on google's partner sites.
Sounds promising, but not for the people who do marketing to a younger audience (teens) who probably won't see much in the way of any success with this program. I guess this does sidestep the Do Not Call Registry because they asked for the call, but how to they stop people from giving away other peoples phone numbers and having them be bombed? I guess we'll know more when it gets closer
I think this could well be the next phase of adsense (to add to the current system) in that you have interested people contacting the advertiser directly. I don't think it will abolish the invalid click problem alltogether because you could still have people contacting without actually intending to purchase. I think this could work really well.