Abstract: A bidding system on a network between suppliers of advertising space in web content for mobile telephones on the one hand, and advertisers on the other hand, to supply advertising space with advertisements included therein to mobile phone users at content download time, bidding being carried out per content page per user download. The bidding system operates by determining real time sales related to a given advertisement campaign; determining a proportion of those real time sales to be applied to the advertising space currently being downloaded; presenting the proportions as bids; selecting a best bid; and allowing the advertisement campaign corresponding to the selected bid to use the advertising space currently being downloaded. The publisher who is providing the advertising slot may continue to be paid on a per click basis.