From Clickz (which, by the way, I call 'Clicksz', not Click-Zee - see: 1980's BBS lingo) -- People are willing to listen to a few ads before getting 411 info as long as the service is free. This goes against the current model LAN line and cellphone companies are using, so the question becomes how long before AT&T, T-Mobile et al switch to ads instead of a fee?
Jingle Networks provides the free 411 info if you'll listen to 2 ads. A few companies have jumped on board with the service, look for more to jump on. It will be interesting to see at what point users determine the ads are too much and bail out of using the service.
Also of interest -- the entire service has been popularized by word of mouth, with 600,000 users per day, according to Lyn Chitow Oakes from Jingle Networks, the company providing the free 411.