how to start carrer in mobile applicaion in .net

Hi,
     If you are aiming for mobile application development, there are many options.

Choose Android - if you already know little bit of java or other OOPs language like .NET etc.
Android is very easy to learn and develop an application if you know the basics of Object Oriented Programming.

Choose iOS - if you are good in c, c++, and pointers.

If you are very eager to know what are the major differences and why to choose android, check out Android Market trends.

But if you are targeting for wide range of devices for your application, then choose android.

If you are aiming at building a mobile application which can run on any hardware or on any platform, then you can choose any of the below hybrid platforms:
1. phonegap (if you are already good in html5 and css)
2. mono (if you already know .net)
3. JQueryMobile (if you are already good in jquery, html5, and css)
There are more than 25 cross platforms to develop mobile apps for all hard wares.

But the major difference between native platforms (android or ios or blackberry) and hybrid platforms (phonegap, mono, jqm, etc):
1.native platforms are faster than hybrid platforms. So don't use hybrid platforms to build heavy applications. They are still in testing phase.
2.hybrid platforms can't enjoy complete native platform capabilities. So you can't really build smart applications with hybrid platforms.
3.hybrid platforms add one extra layer on native platforms, so its little slow.