I am not an usability guru or an expert in usability arena.  But I would like to share my thoughts when I had an application which my team developed for review with few iPhone users.  Surprisingly, I could see lot of things on how people react to the usability of the application.  The group ranged from sparse users to best users of iPhone.

I had to admit that I was unable to digest all the feedback given by the users.  But still I feel all the points given by the users has got a huge value.  I would like to quote some examples from the review.  The application had barcode scanning, the user took the iPhone device and started to place the camera of the iphone to very close to the barcode.  However, after sometime the user managed to scan a barcode.  I felt the necessity of placing a help mechanism to get the users right at the first time. Again that is subjective to the users whether they opt of reading through the help.

Another issue on usability was throwing a registration screen in front of the user.  We had a registration screen and users did not know how to navigate through it.  If we wish maximum number of people to use our application we should cater to the weakest or dumbest request of the user.

Learning is fun.  I understood that the touch screen users try to use their click click mind on a touch and expect it to work as they do in desktop.  This needs to be kept in mind of the designers / developers of mobile application.  Hope this might add 2 cents to someone who needs something about usability on mobile phones.