Please note: I am not, and never have been a qualified lawyer, so any legal issues you may encounter whilst using the following information are not my responsibility. That having been said...

A lot of cell phone network operators are now offering add-ons to help spice up your phone. These include ringtones, realtones (full mp3 versions of tracks) and so forth. This is great, but most of these incur charges which are often outlandishly high (for a 30 second mp3 clip is one example). It's also the case that many of the tunes which people want to add to their phone are their favourites, and ones which they already have full versions of, either on CD or as mp3's on their computers or iPods.

IHowever, you can get the same effects without the charges using some freely available software and your own tracks. And the advantage of this is that you can have whichever part of the track you want, for as long as you want, and you can change it every day if you wish without cost.

What you need:
The track/file you want to use on your phone
MP3DirectCut
The software to transfer the file to your phone.

What you do:
1. Download MP3DirectCut to your computer, and extract the files to a folder of your choice. Make sure you extract all the files, not just the .exe.
2. Find the track you want to use, and copy it to the same folder where you extracted MP3DirectCut above.
3. Open MP3DirectCut, choose File > Open and locate the track copied over in Step 2.
4. Usually you wont want the entire track to use as your ringtone, as you normally only have about 30 seconds or so to answer incoming calls before they are sent through to voicemail. Therefore, decide on a portion of the track that you want. What you have to do is cut out the parts of the track BEFORE and AFTER the part you want to keep. Use the play/stop controls, and the Set Begin and Set End buttons to select each part in turn, then press Delete or click Cut. If it's done properly you'll end up with just the part you want to play. Use Undo from the edit menu if you make a mistake.
5. Save the clip using File > Save All and give it a logical name. This will be the name that shows up in your phone's list of selectable ringtones.
6. Copy the new file to your phone using your phone's transfer software.
7. Now just select the newly copied clip as your new ringtone. Test it and enjoy.

Notes: The software linked to above is freely distributed under the relevant distribution license and only works for MP3 files. For best results, it is recommended that you use tracks recorded in either 128 or 320kbps. When saving the track, try to save to the phone's internal memory to reduce lag time when an incoming call arrives (the track has to be buffered before it can be played, and loading from a memory card increases this time and can cause stutters or the track to not be played at all).

Comments are welcome, and do let me know how you get on. Remember that just because the track is being played on a cell phone doesn't mean that copyright laws do not apply. You should therefore ensure that you own rights to, or have permission to manipulate the files that you are using. But I'll leave that part up to your own judgement, :)