I don't know of any programs to download onto the Iphone, but JBM works just fine on it. Create an icon link (application link) to your front page so you're there in one touch from the front screen.
If you're in an area without coverage, simply use backup screen shot images from JBM. From your home, enter your ballistic info and press calculate. Now take a screen shot of the drop chart to save for future reference. Like this:
To take a screen shot, press the home button and the power button at the same time. The screen shot is saved onto your camera roll. On the saved image, you can zoom in a little bit but the detail isn't good if your initial picture has really small writing. It's better to go back to the program and zoom in for more detailed screen shots like this:
It saves the picture on your camera roll but you can organize your drop chart images into a seperate dedicated folder(s) using iTunes. You can save as many images as you want for as many calibers etc as you want, so calculate several charts with different temperatures etc depending on your expected or generic conditions. I have a different folder for each caliber/bullet. For really long range shooting, you may need to take two screen shots, the first from 0-500 yards, and the second to cover 500-1000 yards. No need to print them out, you've got these charts with you at all times. It's really easy to add/delete or change them at any time.
Hope this helps! I've had my iphone for two weeks and I'm still figuring out all the neat stuff I can do with it. For example, in the calculator function, tip the phone sideways and the normal calculator turns into a scientific calulator in case you want to figure out cosines etc. I'm sure there's also a way to figure out your angle in degrees by using some sort of bubble level application with the iphone's accelerometer.
Did I already mention this is a neat phone?