The contacts on my realtime communication media are all close people - the kind that won't hesitate to ignore my interruption if they are really truly busy. Also, I use the Hindi word "Sunn..." which means the same as (but is not as intrusive-sounding as) "Listen" but it doesn't translate very well in English.

For me, email is more of a documenting system rather than conversation. Also, in my mind, I still consider email to be a medium for formal exchange inspite of the fact that smartphones have made them almost instantaneous, as you very well put it.

Still, to each their own, I guess. Thanks for the insight! :)