Desmond turns himself in to the police, meets Sayid & Kate

As the police officer that Locke hung up on puts down the phone, Desmond approaches his desk and asks to speak to a detective.

Meanwhile, at the police station, Miles is getting dressed for a concert to benefit at his dad's (Pierre Chang) museum. He tells Sawyer that he can still be his date, but Sawyer passes since Charlotte is going to be there.

The officer from the front desk then brings Desmond to Sawyer. Desmond admits to hitting Locke with his car and beating up Ben at the school.

Desmond is led to a holding cell, where is placed between the ones containing Sayid and Kate. He slyly smiles as he introduces himself to Sayid and Kate.

So it became clear here that Desmond wanted to be put in jail so he could interact with Sayid and Kate like he has done with Hurley, Locke and Ben. We get a clearer view later in the episode of his plan later in the episode.