As a third party .NET vendor, it makes sense to choose the easiest and closest route to enter the mobile development, and that would be definitely the Windows Phone or WinRT since both are still based on .NET platform. The main problem, however, is the relatively slow adoption rate which makes it less appealing on the business side. This is understandable because enterprises cannot control what mobile devices their employees and consumers use. Most requirements that we heard from our enterprise clients will be to support at least two of the most owned mobile devices. Needless to say, that will definitely fall to iOS and Android based devices. As we see it, one of the biggest challenges here is multiple mobile platforms support, just like multiple browsers support in the Web development.