I've always liked the idea of 'Ambient Speech', the spoken word equivalent of ambient music.
It's the background sound of a cafe or a bus. A conversational, human noise that lets you know you're alive and not alone but doesn't intrude too much.
The shipping forecast is a great example, and Test Match Special, and baseball commentary, and Dan recently reminded me of Alan Licht's New York Minute which is a splendid example (and you can listen to it on last.fm). And there are some perfect ambient speech moments in Giles Turnbull's lovely sound fragment portrait of London.
I used to think that what you wanted from Ambient Speech was the rhythm of conversation but that you didn't need the meaning, like Charlie Brown's teacher. But I was awake in a hotel room once listening to the sounds of conversation from a corridor and it's deeply frustrating if you can't hear the words. So there have to be words, but it's best if they're slightly abstract and part of something flat and extended. That's why cricket and baseball work but football commentary doesn't. Cricket commentary's like Norfolk, football commentary's like Soho. Or something. You need to be able to tune in periodically, but the sound should be slippy, so your mind can slide off somewhere else.
I periodically experiment with tacking bits of old spoken word vinyl together to make such a piece but it hasn't really worked yet. It's too jarring when the textures change.