Google has announced a new option to bid differently for phone calls versus clicks to your web site with Bid To Call charged on a cost-per-phone call (CPP) basis.
So if you are willing to pay $5 for a phone call but only $1 for a click to your web site, you can now specify so.
The ad position for these are are based on the quality score and CPP price. The algorithm is Ad rank = (max CPC bid x click quality score) + (max CPP x phone call quality score).
How do you set this up?
Then when someone sees your ad and calls you, Google will charge you the CPP price:
Forum discussion at WebmasterWorld.