What OAuth flow should I use in Mobile Application?



If I want my mobile app to tweet on user behalf without using xAuth, what is the alternative?
(Knowing that mobile has a built-in browser).

Now if I have user name and password, what API should I use get an authorization URL, so user - or my application - can open the browser, and user "authorized " my application? ( As ‘Gravity’ app does ).

When - IF - user authorized my application, what API should I used to get user OAuth Token?
(To use it to structure the message sent as a tweet on user behalf).

I hope you can help me, because there is a lot of choices, and a lot of flows. and what steps to follow.

Many thanks in advance.