Okay, so it's been the DS, and the 3DS.  More or less, the 3DS is a beefier DS with 3D capability.  That's all fine and dandy because the DS and 3DS are making a ton of money.  That being said, it's starting to become boring.  With the ever presence of IOS games looming above NIntendo's heads, it becomes a growing concern for nintendo to put their games on those systems.  But they aren't, they just aren't.  It's always been Nintendo(Philips CDI noted) properties on Nintendo consoles, simple as that.  That means that no outside machines other than the ones they own. 

But you can't ignore the present of mobile gaming.  It's here already.  The possibility is here whether you like it or not.  The truth of the matter is that iOS far exceeds what Nintendo could possibly do with a games only mobile machine.  It's a uphill battle Nintendo could not possibly do.  And the threats are there, games on iOS are becoming more and more of a threat.  Ace Attorney is one example of a huge hit being taken away from Nintendo.  It's a touch based game that require no buttons for you to play the game.  It's certainly not the first of it's kind, but it is a noteworthy title to the DS's history.  And it doesn't stop there, phone companies are getting wiser, implementing new strategies with their next version of their phones.  Just imagine one of the phone companies really starting to develop a mobile with the gamer in mind.  It may flop, but if it's not Nintendo doing it, it's not good for Nintendo because one of these days it will be a success. 

As a final thought, I want to say how much effort Nintendo would have to put into making a machine that worked well, and still be a cell phone.  The design has to fit the gamer's needs, as well as sustain the same feelings smart phone users are having now.  It has to streamline like a normal phone and be a gamer's machine at the same time.  It is incredibly hard for them to do, but they have too.  If a successful phone manufacturing company creates it before Nintendo, it would be a repeat of the rise of Sony for Nintendo.  And this time, it may be them to be the next dreamcast(I mean for mobile consoles only).

I would buy it in a heartbeat.

I don't think many others besides hardcore Nintendo fans would, though.

Why would anyome buy a nintendo phone ith no app support besides their games? Look at wp8 struggeling with the lack of support.. And if someone say they should make an android phone; if their games run on android why would i go for nintendo hardware?

no way!mobile gaming...the rather,smartphone gaming(facebook gaming is disambiguous from big success to an easy fail, see Zynga) is popular because games cost 2-5 dollars and some are free

I'm pretty happy with my flip phone. I do not want a Nintendo phone.

I don't think such a device would have a very large market.

No way. That would officially kill handheld gaming forever and cut their income in half.

Today it is 2-5 dollars, tomorrow it may be 34.99.  A serious gaming machine fitted like a normal phone with development cost like a triple A sony title.  What's to stop that from happening within the next 5 years?  If not the next 5 years, the next 10.  There will be someday a machine like this and the way things are going, it will not be nintendo.  They don't have the DNA to create a phone like Samsung, at least we don't see that side of them. 

Hand held gaming is not going to die, simply change hands.  Where Nintendo mobile consoles have reigned undisputed in the past, the day will come when the ultigrations between a phone and a gaming machine collide.  Where are we in technology where we can do this?  Now.  Where in the artistic and design and the grits and balls to do it?  We'll see.   But mark my words, the day will come.

This is a great idea, a Nintendo Phone

with a Ubuntu OS would be great

You have a flip phone, of course you wouldn't want a Nintendo phone.  You don't even count.  Not trying to offend, simply stating the flaw in your logic.