Part of the problem with mobile development is deciding whether or not to actually write a mobile application. This can be a big decision as mobile applications are usually native to a device such as android or ios. At this point the only mobile devices that are. Net based are windows phones. They take less than 10% of the market right now so the path I usually take is with website development.
Most phones are getting to a point where they support touch controls on websites etc. A big advantage to gearing your site towards this is platform independence. You can write a master page targeting different sized browsers such as tablet, phone and standard computer. As always code reusability is the target. Happy coding!