Last August, a start-up Pelago filed for a patent for a "a method and system for providing a pay-for-visit billing model for advertisements." Slashdot explains that the system would use "GPS, Bluetooth, or RFID on your mobile devices to track your travels to see if you wander into a place of business that appeared in an ad shown earlier on your cellphone, PDA, or laptop."
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Pay-per-call Ads in Action
Commentary: The Problem Of Pay-Per-Action Ads
