I think every modern website has app to use it in smartphone and why do you ask that? If there isn't need of app for smartphone than other companies are doing silly things when they put money on developing website's app. As I know bitcointalk don't has even mobile version (I can't use it and have never seen). With mobile we can save mobile data, functions will be better and easy to use but I agree someone who posted here that it's hard to build and intagrate api for this cms of forum.