It has a Super CVT-i transmission the same transmission which comes in the '05+ Vitz. Well, I wouldn't suggest you get a CNG kit for it because it's already a very economical car. If you're getting in between 13-15km/L in the city with bumper to bumper traffic and alot of stop and goes I don't know why would anyone in there right mind convert it to CNG.
People have tried to get CNG kits installed in the 1.0L 1KR-FE Belta/Vitz but it causes alot of problems afterwards, especially because of the inline 3-cylinder 1.0L displacement but I've heard that the 1.3L varients perform good on CNG I haven't drove any Belta/Vitz on CNG but I've heard that they do peform well, can't say anything unless I see and drive one.