yahoomobileAT&T and Yahoo! announced today they are expanding the alliance they began in 2001. The companies will collaborate on developing mobile web sites, and share mobile advertising revenue — in an apparent effort to halt Google’s advance into the mobile realm.

Yahoo! announced its Go for Mobile 3.0 beta at CES (our coverage), which includes a platform for developers. Together with AT&T, this pits the two squarely against Google and its upcoming Android developer platform.

AT&T meanwhile welcomes a partnership with Yahoo! because it gives it a large online partner with experience building mobile applications used by millions. AT&T’s own offerings in this arena have been weak.

This partnership also extends beyond mobile. The two will team up to revamp the att.net web portal, which will now be “powered by Yahoo!” beginning in the 2nd quarter. This will include not only Yahoo! Search, but the My Yahoo! and Yahoo! Mail services.

Yahoo just announced their 4Q results and topped Wall Street’s estimates, but net earnings were down from the year-ago period and 4Q profit fell 23%.

The company named Ari Balogh as chief technology officer today; he previously held the same position at VeriSign, Inc. This comes ahead of job cuts at Yahoo! expected in the coming weeks.

MG Siegler blogs on technology and new media at ParisLemon.com.

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