Some carriers send a USSD balance update message after each call, and sometimes after each data session on prepaid plans. This is very annoying, and SMS blockers won't stop these USSD messages.
I wrote an app to block USSD messages by keywords or regex. Works well for me in blocking my carrier's balance update messages.
My first android app, so please let me know if I can do something better.
Credits to commandus.com/blog/?p=58 for showing how to intercept these messages using the undocumented hook.
App is "com.melkote.quietbalance" on Google App Store. The v1.0 of the app is also attached to this post.