You come across a sticker on a lamp-post, or spot a note in an empty phonebox:
“For a really nice chat, call 0844 . . .”
Out of sheer curiosity (and as it’s not just someone’s home/mobile number - so it’s clearly not a windup at the expense of someone whose number has been spread maliciously), you give it a ring. Someone answers, in a nice cheery voice; you idly converse for a couple of minutes, they crack a couple of inoffensive jokes - maybe they look up tomorrow’s weather for you (if you ask them to, nicely).
You call back the next day, but you get the answering machine - their outgoing greeting is very outgoing, so you leave them a nice message. The day after, you ring and find yourself talking to a different person to the first time you called, but they’re just as nice.