Users of 3 can currently browse only selected internet content on their handsets, known as a 'walled garden', and the deal will provide unrestricted access to websites adapted by Yahoo to suit smaller screens on mobile phones.
"Convergence between the internet and mobile has been much talked about, but this deal will really make it happen," said Christian Salbaing, managing director for European telecoms at 3. "It is going to be fun."
Geraldine Wilson, vice president for connected life at Yahoo Europe, added: "This arrangement gives us a new opportunity to take Yahoo content and services to even more potential users, especially those that might not have ready or frequent access to the internet via a PC."
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