as you know the Mail app in iOS 5 have a rich text editor is there any possible way to use this feature for a regular UITextView ?
The iOS 5 rich text edit control is also present in the notes app in iOS 4 (make a rich text note on the computer and sync it to see).
This is a custom Apple-made control which they use in their own apps, but it is not published in any official developer API. It's probably in the SDK somewhere, but because it is undocumented, even if you find it and use it, Apple will reject your app.
Basically, if you want a rich text control you will have to make your own.
Edit: Try using this: https://github.com/omnigroup/OmniGroup/tree/master/Frameworks/OmniUI/iPad/Examples/TextEditor/. I haven't used it, so I don't know how well it will work. (Link from this question)