The problem with that is that many non-business people don't have audible notifications turned on for email. When I receive an SMS I know it's a real person an

The problem with that is that many non-business people don't have audible notifications turned on for email. When I receive an SMS I know it's a real person and thus important, whereas when I receive an email it's probably a group-buying site email or a server notification or something else not worth interrupting me. Until we get much better prioritization tools, it'll be hard for SMS to replace email.