Dialing a USSD code from a custom activity is straight forward using a DIAL or CALL intent, but listening to the returned result is not due to Android not having proper support for intercepting USSD calls within the platform, but partial though undocumented support exists within the native dialer application.
As a start, look at the PhoneUtils class in the Android source code. The link is for 4.0.3 but I believe this partial support has been present since 2.3.
Specifically, looking at line 217, an intent with the name “com.android.ussd.IExtendedNetworkService” is being composed. So what you need to do is implement your own service that responds to that intent. The service needs to be implemented according to the IExtendedNetworkService.aidl which is a part of the Android framework.
The aidl exposes several functions but the one we care about is the getUserMessage(text) function in that service. The text is the final value returned from the USSD call.
Since the service is binded on by PhoneUtils, then you need to start the service at phone boot up. It also means that any modification to the service will need a phone reboot.
Returning null from getUserMessage will suppress the dialer from showing the USSD result but there’s no way to completely hide the dialer.
You can also use the other functions to change the text shown while the call is in progress
This doesn’t seem to work on USSD prompts(menus), only on final results
Nothing explains code like a code sample, right? So I wrote a sample service and you can take a look at this link.
Inspiration for this post and code came from this Russian blog post.