Is there anyway to disable or change the sound the instance balance reminder on O2 pay as you go makes?

Q: I have recently bought a new Blackberry curve 3g 9300 on O2 Pay as you Go.
my question is.
after i send a text msg i get an instant balance reminder with a very annoying and loud bing bong tone.
i) is there a way to change this tone or turn it off.
or
ii)is there a way to disable this instant balance reminder full stop