Depends what you consider meaningful in life I think. Certainly a nihilist could say so.

I find it difficult to draw a line. Is it meaningful to build smartphones?

Well, I think it is difficult to draw a line or we wouldn't be having this conversation, and everyone's line is going to be in a different place (and move around a bit as they change their own opinions as well). A large part of philosophy is built on trying to decide what is meaningful to do.

I can't give you an answer because I'm not sure what the best answer is myself.