When Slim returns the page from Mitch's mistress, Darcelle, we see a close-up of Slim entering the number on the cell phone. The cell phone is different than the cell phone she was using in the previous and subsequent shots.
When Slim dials 33 the first time, she gets Darcelle, the next time she gets her husband. However, the first time she dials 33, she does it on Mitch's phone. When she dials 33 to get Mitch, it is on her phone.