Where'd you hear that? 2-pop discussion boards, you know you're my best friend.
Of course, using keyframes to adjust your audio levels and effects doesn't make you a sound designer, any more than snapping pictures makes you a photographer.
[Note to self: Last time you had to do this, you linked to freakin' Charlie's Angels. This time, put it on your own damn website so you don't have to ferret around for (seems like) hours trying to find the settings again.]
FCP settings for a telephone effect filter
There are two things that characterize a telephone sound: limited frequency range and harmonic distorion.
For frequency, apply high pass filter (about 300 Hz cutoff, high Q), low pass filter (about 3000 Hz cutoff, high Q), and maybe a notch filter at about 1000 Hz. Play with the cutoff frequencies...
I don't think FCP has any audio distortion filters. If you're not satisfied with frequency filters alone, apply distortion in a different audio program... Or play a clip and record it with a crappy microphone :-)
JM (Thanks, JM!)
Another note: I balanced half the audio levels last night (2AM), and finished this morning (11AM). As I listened to the whole piece through, the first half averaged about 3-4 dB lower than the second. The difference? No traffic or street noise last night. To a New Yorker, that's interesting. To anyone else, annoying. (Which thought did you have?)