There are a few ways of doing this.... a lot of plug-ins, etc. have presets for this too, as mentioned. If you want to do it on your own with EQ and stuff, try drastically cutting the lows and highs, leaving only a narrow band of mids on the track. That will get you close, and you can tweak from there.
Alternately, why don't you actually play it through a phone and record it on the other end. If you don't have two phone lines (most of us don't), try playing it at a friends house and record it onto your answering machine, and record the playback from there, or have someone at home actually record it from the phone.
Or... if you have a feature on your phone service that is like a "virtual answering machine" (Bell calls it "call answer") that takes messages while you're on the phone, you can actually phone yourself from your own line and leave a message on your machine. (or in your voice mailbox, or whatever lingo they use...)
Chris
