LONDON  For years, Internet service providers have watched with envy as the likes of Google, Yahoo and Microsoft sliced up the online advertising pie. Selling Internet access has been a good business, but selling Web advertising has been an even more lucrative one.

Now, three Internet providers in Britain have teamed up to try to obtain a piece of online advertising for themselves. The three companies  BT, Carphone Warehouse and Virgin Media  announced a deal last week with a company called Phorm, whose technology tracks Web users and sends them ads related to their interests.

Phorm said it would set up a new online advertising platform called the Open Internet Exchange, which any Web site would be allowed to join. Proceeds from ads shown on these publishers’ sites will be shared with BT, Carphone Warehouse and Virgin Media, which together represent more than two-thirds of Britain’s Internet access market.

The three Internet providers have agreed to give Phorm access to customers’ browsing records, letting it track a Web user’s every move. That way, the Internet exchange can send an ad directly to a select audience anywhere on the Web, rather than hoping that the user lands on a site displaying the ad.