What could a tie-up of Microsoft (NSDQ: MSFT) and Yahoo (NSDQ: YHOO) achieve in the mobile space? In the release and letter to Yahoo’s board, Microsoft identified mobile as a key areas where the two can “innovate in emerging user experiences.” Both have been busy the past year building out their mobile services and strategies. Here’s some of our coverage of their activities in the mobile space:

Mobile Advertising News:

-- Yahoo And AT&T Shift Strategic Alliance, RestructureTo Ad-Supported Portal From Premium; Revenue Hit

-- Yahoo And T-Mobile UK In Mobile Ad Tie-Up

-- Yahoo To Launch Panama For Mobile In Q1

-- Yahoo Buys Munich-based Mobile Marketer Actionality

Mobile Services News:

-- Microsoft Aims To Create Range Of Mobile Services; No Plans For ‘Microsoft Phone’

-- Microsoft In Process of Acquiring Mobile Music Service Musiwave; Price Around $50 Million

Mobile Platform News:
-- @ CES: More On Yahoo’s New Mobile Offerings

-- Next Major Version Of Windows Mobile To Get ‘Desktop-Grade’ IE6

-- Yahoo Continues Mobile Strategy; No Plans For OS

-- Microsoft Spin-Off Zumobi Launches Beta Of Content App With Zoom-Based UI

-- Yahoo Not Stupid, Will Work With Google And Apple OS’s

-- Yahoo To Launch its Own Mobile Dev Platform; Runs Widgets Within Yahoo Go

Mobile Search News:

-- Yahoo Signs America Movil For OneSearch; 16 Countries Included

--Sprint To Use Microsoft’s Search On Its Service

-- Yahoo Beefs Up Mobile Search, Extends Reach of OneSearch To 14 Countries and Counting

-- Microsoft Set To Launch Trio Of Mobile Search Services Today

Be sure to check out the Microsoft and Yahoo archives.