Swingers

Mike Peters is a struggling actor who left New York to find success in L.A. six months prior. The move precipitated a break up between him and his girlfriend of six years and left him feeling alone and heartbroken.
In the opening scenes of the film, Mike talks about his situation with his friend Rob, another thespian from back east. Mike feels miserable about their conclusions. Afterwards, while on the phone, Mike is coaxed into an impromptu Las Vegas trip by his new best friend, and also actor, Trent to help Mike get over his ex. The trip starts out on a high note with excitement and anticipation but soon takes a turn for the worse when Mike crashes and burns at the casino. Soon after, the guys manage to meet some ladies and just when it seems as if Mike can make some progress and salvage the trip, it all falls apart again and this time Trent goes down with him.
On the ride home, Trent gets Mike to feel better about himself and to look at the positive side of things. Mike promises to try his best to move on.
Now back in L.A., Mike and Rob get together for some golf and to talk shop. Later that night, Mike and Trent are getting ready to hit the Hollywood hills, at their actor friend Sue's apartment. With the vibes feeling right and things going well, Mike and Rob meet up with Mike's pal Charles, yet another starving actor, at a local bar where they admire the beautiful women. Soon afterward they rendezvous with the others and they all finally make it to a party where Mike makes an ill-fated attempt to get back into the game, while Trent gives the guys a lesson in how to handle the opposite sex.
The guys agree to head to their favorite after hours spot and, after watching Trent and Sue effortlessly meet some girls, Mike is clearly shown feeling lower than ever but not yet defeated. Trent and Sue convince Mike that he is in control so he finally makes his move like he's got nothing to lose and he actually meets Nikki and gets her phone number. Success at last, or so he hopes.
The swingers leave the lounge and narrowly miss getting into a brawl in the parking lot, caused by Sue's temper yet averted by Sue pulling a gun which no one else was aware was even a part of his attire. The group splits up but not before angry words are exchanged among friends. Mike is left feeling desolate once again.
To make himself feel better, Mike decides to call Nikki but he blows any chance he has with her when he leaves a series of increasingly awkward and desperate messages. Now he feels as if he has truly hit bottom and he sits alone in his apartment, missing his ex more than ever and contemplating a move back to New York. Rob comes over to console him and, after some serious talk, he feels like it's time to get back in the saddle again.
Mike meets up with the guys at Sue's, where he discovers that he has missed some changes in the group dynamic. That aside, apologies are exchanged and the nightlife once again awaits them. The next stop is a Hollywood night club for swing night. The guys enter through a makeshift VIP entrance in a style that pays homage to Director/Writer/Producer Martin Scorsese.
Once inside, the guys let the good times roll and Mike spots a beautiful woman whom he decides he wants to meet. He gathers all his courage and approaches her confidently. He finds himself in an actual interesting conversation with the young and single Lorraine. They are soon swing dancing and the chemistry between them is incredible. The night ends well and Mike, Trent and Sue head to an after-hours meal to discuss the particulars. Mike finally appears to be on his way to moving on and feeling good about himself.
The following morning Mike receives a phone call from his ex. She wants to talk about their state of affairs, but when Mike decides to answer another incoming call, he is greeted by Lorraine. He has to make an immediate decision as to which path he wants to go down and in a moment that solidifies his regained self-esteem, he puts his past behind him and chooses to take a chance on someone new. This moment parallels Rob's advice to Mike that he gives in the opening scene where he states that girls never call back until you have forgotten about them.
In the closing scene, Mike meets Trent for coffee and they enjoy one more good heart-to-heart while Trent is brought down to earth by a reminder that even when you have got it, you cannot win them all.

Question: Who calls Mike to discuss their state of affairs?
Answer: His ex