Despite being textual in nature SMS has by social convention turned into a synchronous protocol. Common scenarios: * A bunch of people are driving separately t

Despite being textual in nature SMS has by social convention turned into a synchronous protocol. Common scenarios: * A bunch of people are driving separately to an event. One of them is severely late. It is likely that the late person will receive an SMS to ask where they are. * Use as a pager replacement makes it odd to send a text at a weird time (especially for on-call employees, for instance). An on-call nurse I know was annoyed after a group text conversation occurred at a late hour.