When I started at KCOU, an in-studio light flashed whenever anyone called the request line. Some staffers, however, argued that it was too easy to miss calls when the phone didn't actually ring. For a time, then, the request line phone actually rang, resulting in on-air scenarios like this:
Me: I'm about to give away two tickets to see (a local band) at The Blue Note tonight. When the music starts, please be the first caller...
(The request line phone started ringing.)
Me (answering the phone on the air:) But not yet! (After hanging up:) When the music starts, the first caller will win two tickets...
There are drawbacks when your station sounds like it's hosting a never-ending telethon.