Blended winglets (the smooth curvy ones) are designed and sold by Aviation Partners, who Boeing have a shareholding in. They have some patented design stuff on the winglets. They sell them to airlines both as customer-furnished equipment which Boeing then installs on the production aircraft, or as retrofits for later installation.
They've only so far done blended winglets for -700s and -800s, and are trying to get the -300's certified.
I heard they are looking at other types (MD-80s), and then maybe widebodies.
Apparently the blended winglets are a lot better than "normal" wing-ends, and somewhat better than "kinky" winglets (in fuel efficiency, maintenance savings due to reduced engine thrust, and in obstacle-limited or short airfields). So we might see them on 777s yet, but probably not for a long time. Maybe 767-300s first.