I love my mobile communicator - iPhone 5 and iPad 3 right now. And, they are super handy for film production and make life a whole lot easier. I've compiled some of my favorites and please let me know if there are any that I am missing or that you'd reccommend.
Production: Movie Magic Scheduler -- Love this app! I am able to swing schedules arounds and really customize it to my purposes. It's helped me organize and be flexible and I'm able to send/receive with others on my team. You are also able to include storyboards/images to reference when you are shooting the scene. This was incredibly helpful when I was shooting 20 promos a day where each frame was a special effect or comp. I was able to pull up the board when needed and quickly switch around the order when scheduling conflicts occurred
TelePrompter: ProPrompter -- (works great w/ an eyeliner)
Reciepts: Genius Scan -- It's a great on the road app where you can take pics with your phone and creates a pdf doc for the end of the job.
If you're yearning find out more fun mobile filmmaking gadgets - check out - Handheld Hollywood