In 2006, Southwest Airlines (Flight Code WN) began marketing ATA's two-letter TZ Coded Flights. ATA's dependence on the Southwest network continued to grow in 2006 to where ATA offered over 70 flights a week to Hawaii from Southwest's focus cities in PHX, LAS, LAX, and OAK. Additional connecting service was available to many other cities across the United States. Plans had been announced for ATA to offer exclusive international service for Southwest by 2010. In 2006, ATA announced its intention to purchase nine widebody DC-10 aircraft from Northwest Airlines. Southwest took over all ground operations for ATA at MDW, OAK, PHX, LAX, and LAS. These contracts provided that Southwest ramp personnel would now handle all ground operations for ATA (loading of aircraft, ground servicing, etc.). The details of these contracts were not made public, but represented Southwest's and ATA's growing codeshare relationship.