...dismissed in favour of backing WP7 because of concerns about how quickly Nokia could develop "a third ecosystem", said Elop.
For Microsoft, the tie-up with Nokia offers the chance to accelerate a nascent platform - launched with much fanfare last year but which has not yet made a serious dent in rivals' market share.
Last month, analyst house Canalys reported Android had overtaken Symbian as the world's most popular smartphone OS - grabbing almost a third of the market. Apple's iOS was third, with 16 per cent market share, while Microsoft - with WP7 and its legacy Windows Mobile platform - claimed just 3.1 per cent of the market.
Commenting on the Nokia-Microsoft tie-up, analysts said Ballmer is likely to be the happier of the two Steves - but noted that Nokia's options to get back in the smartphone game were limited.
"It's a good deal for both of them," said Nick Dillon, analyst at Ovum. "There are probably more benefits to Microsoft - in that they get a very strong hardware partner to help advance their platform. But Nokia gets the ability to get quickly back in the game and compete at the top level of the smartphone market with a quite advanced smartphone operating system so there are benefits for both of them."
"Nokia needed to do something drastic - if they'd waited for MeeGo, which was looking like it was going to be ready towards the end of the year, it would have been pretty disastrous," he added. "They need to make up as much lost ground as possible."
Forrester principal analyst Ian Fogg, added: "This is a massive win for Microsoft but this gives Nokia a credible smartphone platform in the market. Recently their smartphones have been differentiated in the market but they've been...