USSD (Unstructured Supplementary Service Data) protocol is used by the GSM network to send data to a phone over a real-time connection. One of the most common usages is the network provider sending back prepaid account balance notifications after every call, SMS, and data connection. On windows mobile phones, this notification comes up in a balloon at top of the screen with a loud and annoying notification sound.
In case you don’t bother for these notifications and want to get rid of the annoying sound after every call, set the following registry
This will disable all USSD messages popping up on the screen. Some network-specific commands (mostly starting with # or *) which brings back a notification or a menu will also not work after this change.
Another alternative is to just disable the notification sound associated with USSD messages. This can be done using registry
This will allow the USSD messages to come up on the screen but without any sound.
Both the above changes might require (depending on OEM implementation) a reboot.
Note: In case you don’t have any clue how to edit the registry on your phone, there are quite a few registry editors for windows mobile available. This is one of them.
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