The "Hills" star has landed a cameo role in the romantic comedy, which boasts an all-star cast including Sandler, Jennifer Aniston and Nicole Kidman.
In a post on her Twitter.com page, Montag writes, "I was just cast in my first feature film comedy! I start filming Monday!!!!! This is one of the best days of my life!!! Getting ice cream to celebrate."
The movie is set for release next year.