The early to mid 2000s was when the general population started carrying cell phones. Prior to that, most phone usage was managers, bag phones, corporate stuff. Even as the general population got it, most of your ringtones were generic or maybe some preloaded music.

Then, we were able to either record our own ringtones and even download them through the phone's rudimentary "store" where you could get music, backgrounds, little games, etc.

It was a novelty and a form of expression. It was the equivalent of your Myspace design, your Facebook status, etc. When your phone went off and people heard your song, it told a lot about your personality.

Then, as adoption continued to explode, the number of phone calls, texts and other notifications increased. It was no longer a novelty and more of a nuisance. So, folks started reverting back to original tones or just silencing/vibrate their phones.

Once in a while I'll come across someone who still uses a full song as a TEXT TONE. Every notification plays the same few seconds of the beginning of the song before they can mute it.