SharePoint Server 2010 SP1 authenticated through AD in Smart DEvice

Hi, I have some question from customer.

He used SharePoint Server 2010 SP1 to do the portal. he need to display in smartphone/device like iPAD, Android.

For his question, he need to authenticate via AD (2008 R2) in one time. How to config it.

Because they already try authenticate via AD. it will show 2 times for authenticate. someone suggest him to do the Form-based Authentication. that is the same. no convenience.