There is a multitude of resources covering the topic mobile learning - here are just a few to get you started.
Mobile Learning 101
By Judy Brown
ASTD TechKnowledge 2009 Handouts
Learning Circuits Articles
M-Learning Devices: Performanceto Go
By Clark N. Quinn
It's not really about the devices, though. It's about their capabilities.
Authoring Best Practices for Mobile Learning Content Development
By Brad Crain
When developing content for mobile learning, SumTotal suggests following these guidelines.
Thinking Differently About Mobile Learning
By Cheryl Johnson
Too often when we think of mobile learning we think in familiar terms: modules, quizzes, tests, assessments.