Thanks for the suggestions. However, I called Delta here in Sweden and they no longer had the deal when you can go on an unlimited number of flights during 30 days. Instead, one could buy 3 coupons for 509 USD, where 1 flight route within the US is 509/3. This price was when booking the transatlantic flight, Sweden to NYC, through Delta. And I think I can find better prices on transatlantic flights through other companies than Delta. Plus, why buy these coupons when ata.com flies NYC-LA single for 119 USD?
Let me know what you think!