European carrier T-Mobile has partnered with Yahoo!, replacing Google, as its preferred provider of Web services in Northern and Central Europe. The deal was announced at the Mobile World Congress. Although financial terms were not disclosed, Yahoo! says it will reach nearly 90 million mobile customers through the agreement, which covers T-Mobile users in 11 European nations including Britain, the Czech Republic, Germany, Hungary and Poland, where the two had an existing deal. T-Mobile is the mobile arm of Deutsche Telekom.

The agreement will begin at the end of March, when T-Mobile’s previous deal with Google expires.

Yahoo! also said the deal brings the number of mobile subscribers within its reach due to carrier partnerships to more than 600 million. During this year, the company said it plans to focus on joint marketing efforts with carrier partners to convert mobile customers to regular users of Yahoo! services on their mobile phones.

In more Yahoo! news, the Internet company has formally rejected Microsoft’s buyout offer, saying that “after careful evaluation” the board decided that the offer was not in the best interest of its shareholders and that it “substantially undervalues Yahoo!.”

Late last week, Microsoft bid $44.6 billion for Yahoo! in its effort to expand its reach in the Internet space. Microsoft urged the company to reconsider the bid.