I disagree that the value of a desktop is negligible - for me, the "killer feature" of facebook messaging, which I use the same way WhatsApp is used, is that I

I disagree that the value of a desktop is negligible - for me, the "killer feature" of facebook messaging, which I use the same way WhatsApp is used, is that I can type on my desktop with a keyboard when one is available, and continue the conversation on mobile when I leave my desk. SMS doesn't have that, nor does WhatsApp, but I find it very valuable.