You need to work on that. Everybody knows that only bad comebacks end with "or something."
If I were trying to diss him, I would have said something to the effect of:
18days: "When I get one I'll jsut hang around places teenage girls congregate and use it all the time. I hope it blocks SMS too."
Me: "Why? So you can stalk them without worrying about them calling 911?"
You see, it's much funnier if you don't try to use what he finds funny against him (i.e. blocking peoples' calls to cause confusion), instead try finding embarrassing alternate motives.