Should players always have these conversations via phone, rather than text or email? I would think so. But on the other hand, it seems odd to arrange a time to talk with a coach, or to play phone tag by trading voicemails, only in order to tell him "no." A thoughtful email or text could say what needs to be said, and not put a coach in the position of having to make an immediate (and maybe emotional) response.
As I said, I would think these conversations need to be via phone. On the other hand, schools have turned my son down via text and email. (Expressions of serious interest usually are by phone, but not always.)