Well?
If you wanted a ringtone that’s not commercially available, could you make your own without special software?
Would this be a fair use violation?
Not without special software. Most phones now use MIDI, .QCP, or .AAC (for the newer phones) as audio formats for ringers. Google for it and you’ll find utilites you can use. Some websites will even do the conversion for you if you register as a member. As far as the fair use thing, I’d guess that since it will only be a small portion of a song, you’d be OK.
What kind of phone do you have? As Flander pointed out there’s a bunch of different formats for ring tones anymore.
Personally, I have a Motorola v60i which just uses uhm…midi? (just notes, represented by letters and numbers, and something else for sharps, flats and length). I can go into the menu section to make a custom ringtone, follow the instructions in the manual and compose my own ditty.
I had my friend transpose the hook from “Nuthin’ but a G Thang” for my phone and I must say it’s pretty sweet.
I was able to find a bunch of sites where people post the “code” that would produce the desired effect. None of them had any good songs tho 
But yeah some phones do require special software. Mine doesn’t happen to need it, but I also have a pretty weak ringer.
I do it with my Motorola V300. I do use special software to edit the songs (from CDs I own and have ripped to my hard drive in MP3 format) down to 15-20 seconds for a ringtone, I don’t think you’d want the whole song - it would take up a lot of room. I use Sound Forge which came with my Sony computer. Once I have a shorter clip I save it to MP3 format and either upload it to my website then enter the URL on my phone and it downloads onto my phone so I can use it as a ringtone, or I can use a data cable to transfer the song to my phone from the computer.
I did it this way because I didn’t like any of the ringtones T-Mobile or Motorola offered.
I have a Samsung and can do it. Samsung uses .mmf files (which I believe come from Yamaha). I use software to trim down an .mp3 to 10 sec. (that seems to be the limit on the upload). Then I use some software to change the mp3 to a mmf file. I use my infrared port on my phone with my laptop and use (I think) a program called EasyGPRS available from Samsung.
It seems like a long process, but really is pretty easy. It does voices singing etc.
The software I use is all shareware of freeware and easy to use. I don’t really know about the legality of using a song like that though. While I use my own CDs, I don’t know if I can legally use the song like that.
Anyone?