In addition to this, calling can be very time consuming if done manually, prompting many people to switch to an automated dialer such as Mojo or Calltools.

@Dennis Pressey Jr except that a phone call interrupts someone's day whereas a postcard can be dealt with at one's leisure, voicemails also are looked at promptly by many people as it is possible that they are important. 

Your comments have prompted some introspection.