BTW, here is an example of the T&C from a typical Song promotion. The way it is worded, you would be excluded if you purchase 2 one way tickets on Song's site or an open-jaw on DL's site.
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terms & conditions
All Song flights are operated by Delta Air Lines. Earn one 10,000-mile bonus for a flown round-trip ticket between New York (JFK), Los Angeles (LAX), San Francisco (SFO) and Seattle (SEA) purchased at flysong.com. Enrollment and travel must be completed by September 30, 2005. One bonus per SkyMiles member. Enrollment is required. Visit flysong.com/coasttocoast to enroll. All SkyMiles program rules and conditions apply. To review the rules, visit delta.com/skymiles. Please refer Song or Delta representative to: G*9706/36-24.