But Tom's point is still worth making: when a four-letter base call (e.g. "WRRR") is in use in one broadcast service, whether suffixed or not, it can't be used in another broadcast service, whether suffixed or not, without the permission of the existing user of the base call.
In other words, while "WRRRFM" and "WRRR" are different calls, the Rockford station could not have returned to the "WRRR" calls without the permission of the licensee of "WRRRFM." (And until the rules changed in the eighties, the Rockford station could not have returned to the "WRRR" calls at all, so long as "WRRRFM" was being used by a different licensee in a different market.)
Or to use another example that's popped up in this thread: even if NBC changes the callsign of channel 4 in New York from "WNBC" back to "WNBCTV," anyone else wishing to call their radio station "WNBC" or "WNBCFM" or "WNBCLP" would still need the permission of NBC to do so.
An interesting sidenote to this: it's my understanding that the decision about whether another party can reuse a base callsign rests with whichever party has controlled that base callsign the longest. So if I want to call my new station "WABCFM" or "WABCLP," I'm pretty sure I need to be asking Disney for that permission, since it's controlled "WABCTV" since 1986, while Citadel has only owned "WABC" for the last couple of years. (I may be wrong about this; it may actually rest with whichever license has carried that base call the longest, in which case the WABC situation gets massively confusing, since I'm pretty sure WJZ and WJZTV became WABC and WABCTV, respectively, on the very same day in 1953.)
In other words, while "WRRRFM" and "WRRR" are different calls, the Rockford station could not have returned to the "WRRR" calls without the permission of the licensee of "WRRRFM." (And until the rules changed in the eighties, the Rockford station could not have returned to the "WRRR" calls at all, so long as "WRRRFM" was being used by a different licensee in a different market.)
Or to use another example that's popped up in this thread: even if NBC changes the callsign of channel 4 in New York from "WNBC" back to "WNBCTV," anyone else wishing to call their radio station "WNBC" or "WNBCFM" or "WNBCLP" would still need the permission of NBC to do so.
An interesting sidenote to this: it's my understanding that the decision about whether another party can reuse a base callsign rests with whichever party has controlled that base callsign the longest. So if I want to call my new station "WABCFM" or "WABCLP," I'm pretty sure I need to be asking Disney for that permission, since it's controlled "WABCTV" since 1986, while Citadel has only owned "WABC" for the last couple of years. (I may be wrong about this; it may actually rest with whichever license has carried that base call the longest, in which case the WABC situation gets massively confusing, since I'm pretty sure WJZ and WJZTV became WABC and WABCTV, respectively, on the very same day in 1953.)