Well, I think I've told this story on this board before, but it's been awhile. So, here goes. (Sorry in advance for the long post, but it's a long story.)
Back in about 1980, when I was a Jazz Music major, we had a music theory professor who was all about the concept of training people to have perfect pitch. Of course, we had to learn relative pitch, too (as is the case in most music theory classes - and as has been mentioned already). But this guy wanted everybody to leave his class with perfect pitch. There would be a grade assigned at the end of the class, and it would be strictly pass or fail, and it counted for quite a bit of your grade, too. He would test you by giving you a piece sheet music to sing, and you had to sing it in key.
I promptly figured out that it would be a process of simply "memorizing" a particular note, and then using the "interval training" that we had learned to find the starting pitch of the song. So, I set out to find a "reference pitch" that I could use. Well, I discovered pretty quickly that the entire campus was lit by florescent lights, and they all hummed. Since most "120 volt" circuits actually deliver a wee bit LESS than 120 volts, it turns out that the pitch that they actually produce is almost a perfect B flat. So, the first thing I tried was to simply cue myself off of the florescent lights in his office, when I would go to see him for our weekly meetings, and derive my reference pitch from that. It worked fine for awhile. Then one day, I showed up at his office and he had turned the florescent lights OFF, and had switched on an incandescent lamp in the room. Uh oh. BUSTED!!!! Needless to say, I wasn't anywhere near close to the correct pitch on that particular day, and he was clearly onto my little scheme.
Time for plan B. I had a little electronic tuner at home that I used for tuning guitars. In those days, you didn't have the tuners like today, where you simply plug your guitar into and it would read the pitch and tell you if you were sharp or flat. This particular tuner was just a devise that produced an annoying electronic buzz, at whatever pitch you had it set to. You would then tune your guitar to match the pitch. Every night, before I would go to bed, I would set it to my reference pitch (an "A" or whatever - I don't remember which reference pitch I actually chose), stick it under my pillow, and listen to that annoying "eeehhhh" sound for a few minutes before I dropped off to sleep.
The next time I went to meet with the professor, I pictured that "eeeehhhhh" sound in my head, calculated the relative interval from my reference pitch, and started to sing the song. And I nailed it! And I did so the next time, and the time after that. Everything was going well. Unfortunately, one day I showed up for our weekly meeting and started to sing the song, and found out that I was way, way off. Like a fourth or something. Not even close. And I couldn't figure out what happened, either. I could CLEARLY hear my "reference tone" in my head. But somehow, when I made the calculation in my head and started to sing the song, I was nowhere NEAR the correct pitch.
When I went home, I pulled out the tuner and checked the pitch against a keyboard that I had at the house (a Farfisa organ). The TUNER was not on pitch! I discovered that the battery had went almost completely dead, and the pitch of the tuner dropped dramatically as the battery went down. I replaced the battery, checked the pitch, and everything was back on track. In fact, I was able to re-memorize my reference pitch, get the passing grade at the end of the class, and everything was all good. Of course, I never bothered to continue to refresh that "reference tone" in my head. And today, I couldn't listen to something and tell you what key it is in. But I've noticed that, when I sing a song that I've heard on the radio, or whatever, it's always in the correct original key, so I'm obviously still REMEMBERING the actual pitches that I've heard. I know that I could relearn a reference note if I could find any reason to do so. But I can't honestly see why that would be of any value to me, so I don't bother with it.
Bottom line, if you want to teach yourself perfect pitch, you certainly don't need a $140 CD program, you just need a cheap electronic tuner -- and remember to keep your batteries fresh!!!