I don't know about the iphone, but I have been able to do that without any trouble with my android phone.
Here's how it works on android: Using the opera browser on the android, go to the ifly website and download an update package to the root directory of the sd card. Then plug the phone into the usb port. On the phone, select the option to use the phone as a storage device. The ifly recognizes the update package as if it were a thumb drive.
Don't know if there's a similar function on the iphone.
Good luck.