My boss had me just start looking into what it would take to start developing a mobile app. Seems like each device runs a different OS (and/or version of OS) and needs to be programmed in a different language (I might be exaggerating here...it's just overwhelming). I got most of my help researching here on Code Project. Start by reading articles in
The Mobile Zone[
^] which is found under the Learning Zones section.
Also try google. There are some tools out there that will help convert from one platform to another, but if you are interested in programming for the iPhone or other iOS devices they have pretty strict rules that you need to program with Xcode on Mac in Objective C.
Hope this helps get you started.