You need FB Burrito, which is the upcoming release of FB, for mobile development. Burrito has out of the box support for creating and debugging mobile applications on device which FB4 lacks.
Gurdeep - do you know if there is any iPhone support off of FB Burrito. I have not seen any.
I would assume that you want to know if the applications built using FB Burrito are supported in iPhone when you say, "iPhone support off of FB Burrito". If that is so, yes, you can use FB Burrito AIR apps in iPhone, if it's running on Android OS platform.
another link which I came across:
Another step by step approach along with screen shots:
The public preview release of Flash Builder "Burrito" does not support packaging for iOS.
We are working on this and intend to have support for Google Android, Apple iOS and RIM Playbook in due course.
If you would like to access a later build of Flash Builder to see how this is progressing you can sign up for the private pre-release program here: www.surveymonkey.com/s/flexprerelease
Group Product Manager, Developer Tools, Adobe