Evelyn asks Charlie if there's anyone he hasn't slept with in the 310 area code. Los Angeles County has over 10 area codes. Cities and communities usually change area codes every 10-20 miles in LA County. Despite being over 30 miles apart, Beverly Hills (where Evelyn lives) and Malibu are both within the 310 area code boundary.
Evelyn's question to Charlie was, in fact, "Is there anyone in the 310 area code that you have not mounted?"
Episode title spoken by Charlie, to Alan.