If you dont have a memory card or dont want to bother installing a ringtone app you can check out
www.myxer.com..its absolutey free. they will text you anyringotne you want that people make or you can make one yourself using anytype of music file of your pc. its easy to sign up and even easeir to make.
I use both myxer and a ringtone program. Good thing about myxer is the abilty to make wallpapers and stuff too. but the MusicTones allows you to do it on teh go.