Winglets will be an option for all of the 737NG aircraft only. They are currently developing kits for the 757, and 767, and older generations of 747's with a company called Aviation Partners. They are installing all of the sthrengthening components on the 737, so all are capable of an easy addition of the winglets. I know of Happag Lloyd, and South African Airlines ordering them for their 737's.
At Pope, where not happy, until you're not happy!