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 ...
I'll clean it up and put it on GitHub in a few days, I love open source!
In the interim, everything you need is here:
(You can translate it quite well with Google Translate)
I want to link to that...