I've found that the most effective way of regaining focus, is to find something real to do or think about, and write them down as a list. When a time of idleness comes, check the list and occupy the mind with it.

My phone easily distracted me when I'm idling in the middle of some task, for example, waiting for a compilation to finish. But when I'm practicing music, despite my phone being always on as the metronome, I don't get tempted at all. There's no need to fight an urge of browsing the internet.

I have found that the addiction to internet is not really that strong; it cannot compete with what I really want to do. So, as long as I don't let the idleness creep in, I can keep my modern smartphone with me.