I know for a phone with Verizon's basic UI, you press one of the soft keys which will open Options and then one of the options will be to save sound or ringtone or something of the sort, then you just go to your ringtones and set it as the ringtone.

Of course it is probably different for every carrier and UI.

Right, I probably should have mentioned that before: if it helps, my phone is a Sprint LG Rumor^2 (at least that's what it said on the box/instruction manual).

Yeah, I didn't see any option like what you suggested, but thanks for helping anyway!