boeing 737s serve markets previously filled by md90 airliners
on most narrowbody aircraft and some airbus a300s and a310s the flight attendant call button and the buttons to control the reading lights are located directly on the psu while on most widebody aircraft the flight attendant call button and the reading light control buttons are usually part of the inflight entertainment system
 international flights generally have either a twoclass configuration or a threeclass configuration depending on the airline route and aircraft type