So the handheld market is pretty divided these days. The dedicated handheld console market is completely owned by Nintendo. And IMO is a waste of time going up against the name and first party portfolio of Nintendos handhelds.

Then you have the Smartphone market. Arguably bigger than the dedicated market now and gaining more ground everyday.

Moving to the Xbox a moment, of which Microsoft have gained incredible fan support and are now no longer an also ran like last gen, They have the biggest online service available with the most ddicated userbase which more than doubles the revenue taken by any other console manufacturer.

This said Xbox Live gets alot of exclusives and has a huge indie game list, without much effort anymore thanks to the huge revenue it makes compared t its rivals.

Microsoft are building a handheld platform already. With the help of Xbox Live. WP7 and Xbox Live are gaining impressive exclusives already. Tenticles for example wipes the floor with Angry Birds and is reviewed by all users who have bouught the game as such. There is another 14 Exclusives to relase this year on the platform, some of which are multiplayable online. 

Playing online via WP7 Xbox Live is a big deal. Microsoft have nailed down the tech to make this possible on a 3G service.

Microsoft have also entered into a deal with Nokia ( who even now sell more Smartphones WW  than any other company ) which should do them the world of good getting WP7 into more consumer hands. China for example has only 1.7% of phones sold as Iphones. Yes 1.7%. Nokia owns China. And the latest info says Nokia is bringing WP7 to China for the first time.

Xbox Live shouldnt be underestimated, it has the pulling power to get devs interest. Add to the fact that any 360 owner can continue getting gamerscore on any WP7 device and Microsoft have a very good handheld platform in the making. 

Microsoft would be silly to make a dedicated HH now, the WP7 platform has huge gaming potential and if N.O.V.A. 2 releases on the platform with the online multiplayer that is rumoured to be coming then the US and parts of Europe will seriously look at this platform with a big smile. Those who dont know N.O.V.A 2 is like Halo on Iphone but with no online multiplayer. 

Microsoft have a big chance with the online service of WP7 Xbox Live to make WP7 a great handheld alternative.

If they keep building as quick as they are already ( if you have a WP7 youll know what I mean ) then IMO Xmas 2012 will look very different from this year.

So yes, Microsoft already have a handheld and have a great name behind it.

Considering the psp went up against Nintendo and did a breath taking amount, sure it failed when compared to Nintendo but on its own or when compared to other attempts at Handhelds, it did stellar. So it's not completely hopeless going up against Nintendo, just as long you are not wrapped on who finishes "first".

I agree that smartphones is the black when it comes to handhelds but the truth of the matter is; they will never compare to a dedicated handheld system. Sure some games on phones are becoming more in depth and better than angry birds pick up and play style games, but still, the reason why people pick up a DS/PSP and will pick up a 3DS/vita is because they know what they are getting and they know what the machine in their hand can do. I'd rather play a game of Fifa on a psp/vita than on an Iphone, I'd rather play Tekken, streetfighter on a psp/vita than a phone.

Also, if I want to play an Uncharted, a Mario, a Kirby etc, there are only possible on a Nintendo/Sony handheld.

Though with all that said.

MS doesn't need to step outright into the hand held market, the phone affair is just right up their alley.