Two playlists here. The first being the multiplayer "You have discovered X" that only takes a couple seconds. Both playlists feature Leonard Nimoy and Sid Meier doing their thing:
Download with your Android phone, after installing Random Ringtones Manager, of course:
The next one is the single player version of the tech discoveries. These can sometimes be long enough to be full on ringtones, so I'll tag it as such, but you can use them either way of course:
[Ringtones] Civ IV's Tech Discoveries (92 Ringtones) 5.5MB
Don't have Random Ringtones Manager? Download it for Android. Once you have it installed, click on the playlist link above from your phone and RRM will take care of the rest. Once you activate the playlist, a random ringtone from this playlist will play every time you get a message!