However I do not see the real benefit for Nokia. They're gonna lose most of their identity in such move.
Actually, there's a lot of benefit for Nokia in such a move. OEM quest for identity in software is understandable but awfully misguided. They (Nokia, SE, and even HTC) are strong in manufacturing and, more or less, design. And instead of focusing on these strengths what did they rush to do? Make software. Why in the world would they do it better than Microsofts, Apples and Googles of this world, with tons of IP, skills, competences, cash and tens of thousands of developers worldwide? They can't. It's not cost effective, and it's a failed strategy leading to mediocre produts. Nokia is a testament to this, SE is another one, and Motorola almost disappeared by stretching themselves too thin until they dumped their fruitless efforts and joined an "ecosystem" (God, I hate this word).
One may argue that HTC is a successful example, but it's early to tell. Sense (and previously TouchFlo) helped them sell more phones, but that was when the OSes they used were deficient in so many ways and looked ugly. The more Android develops the more Sense will be turning into an annoyance that slows down phones and delays updates. Or look at SE. Their vast "differentiation" efforts are making them a sick joke in the Android world - they constantly delay phones and release them with the-day-before-yesterday's OS versions. Is it helping them? I don't think so. Or look at Samsung, they are successful, but do you think people buy their phones because of its brilliant whatever-it's-called UI thingie? Would it prevent anyone from switching to an HTC? Anyone? Moreover, if Nokia came to MS, MS
themselves would build them a custom UI if need be.
And really, wouldn't you wish they spent money and resources on developing better phones? Purchasing better cameras? Faster NAND flash? Developing better drivers?
Some ten years ago, nobody cared about operating systems on phones - did it prevent Nokia from differentiating itself? Not at all. And it's not like people bought their phones because of some brilliant UI or "value adding" software. They bought their phones because they were thinner, lighter, better looking, whatever. I just don't see why they can't concentrate on that and try to kick some Taiwanese butts.
So, here's your (and their) benefit, you name it yourself:
PS: Personally, as an ordinary consumer, I also would like to see the quality of Nokia hardware combined with WP7.
Does anybody remember the history of HTC? They were an ODM nobody knew. At that time, MS decided that mobiles should be smarter and started building an OS for this. They tried to approach the big guys like Nokia, SE and Motorola, of course. And got rejected vehemently. Because Nokia e.a. thought that software on phones is too important to have it made by someone else. They were scared ****less of the very idea that people may buy phones because they run Windows rather than because they are made by Nokia. So MS went to an unknown ODM in Taiwan, while Nokia tried to go it alone (well, in a consortium with others, which of course shattered into pieces). Were are we now? Moto - almost disappeared, and still struggling. SE - performing poorly. Nokia - losing market share, almost non-present in high end. HTC? Making almost as much money as Nokia. Samsung? Doing rather well, too. Lesson? Don't try to beat others in a game you can't play well.
Now, the big question is, of course, which "ecosystem" to join. WP7 is unproven, new, doesn't allow customization (although I'm sure MS can be pushed over a bit should Nokia wish to join), costs money. On the other hand, it's fully supported by MS, looks and works better, you can make agreements with the maker. Android - free, open, all you need is download source code and have a go, huge market share already. On the downside, crowded market, attracts tons of low-end makers (thus prices are bound to go down), needs a lot of work, using it doesn't put the maker into any contractual obligations whatsoever. They can dump it tomorrow if they wish and you have nobody to complain to. Dubious IP cleanness.
And then there's a fundamental business model conflict between Nokia and Google. For Google, the more phones can access google.com, the better. It doesn't matter how they work, how they do it, who makes them, whatever. This is best achieved when phones are dirt cheap. So they'll always be happy when cheap phones pop up everywhere with their OS. For MS it's vastly different. They can charge money for their software only when the products using it are expensive so the price can just "hide" in the total price. Thus MS (and Apple) are working towards the same goal with Nokia, while Google will work against it. Google already hurt Nokia, by the way and cost them hundreds of millions (if not billions, I don't remember) in satnav. Nothing personal, that's just what Google's business.
I don't know what I would choose, really. There are pros and cons to both. But MS is a much more natural partner for Nokia, there's no doubt about it.