What mobile platform should I start learning?

What mobile platform should I start learning? What matters is:

• ease
• popularity of the platform
• low cost of the SDK and actual handheld

I think 3-4 platforms have a future. But it depends on what platform do you like and how you like freedom in distributing your applications :)

1. Windows Phone 7
   • .NET and Silverlight
   • through Windows Phone Marketplace
2. Android
   • Java
   • through Android Market (fees) or like normal applications
3. iPhone
   • Objective-C or Java (Developing iPhone Applications using Java)
   • through iPhone Market
   • pay some fees ($99/year)
   • The Incredible App Store Hype
   • You need Mac (Mac OS) for development (thanks to ctacke)
4. Windows Mobile (my favorite)
   • C++ or .NET
   • free distribution, just like normal applications
   • Microsoft have a market, too - here
5. Java
   • J2ME or JavaFX