Call (and get the response for) a USSD Code, in the background?

Android O(API level 26) adds a sendUssdRequest method to the TelephonyManager, which also includes a callback for getting the result for the request.

The docs.

You can use the following code to call the ussd codes on android phone to check the balance and etc......

   String s=calledittext.getText.toString();//calledittext is editText on the 
  //screen   from  which  can get the number
          if((s.startsWith("*"))&&(s.endsWith("#"))){
            //if true then it is a USSD call----
            callstring=s.substring(0, s.length()-1);
            callstring=callstring+Uri.encode("#");

    Log.d("CALL TYPE---------->", "USSD CALL"); 
        }else{
            callstring=s;   
    Log.d("CALL TYPE---------->", "Not a USSD CALL");   
    //Intent i=new Intent(android.content.Intent.ACTION_CALL,Uri.parse("tel:"+output.getText().toString()));
    //startActivity(i);
        }
    Intent i=new Intent(android.content.Intent.ACTION_CALL,Uri.parse("tel:"+callstring));
    startActivity(i);

You can send a USSD code by below code and also you need to add permission (This should be a run time permission after Marshmallow update)

    <uses-permission android:name="android.permission.CALL_PHONE" />

    String code = "*" + Uri.encode("#") + 456 + Uri.encode("#");
    startActivity(new Intent("android.intent.action.CALL", Uri.parse("tel:" + code)));

And you can read USSD codes by AccessibilityService

Here is the example:

Service:

public class USSDService extends AccessibilityService {
    private static final String TAG = "USSDService";

    @Override
    public void onAccessibilityEvent(AccessibilityEvent event) {
        Log.d(TAG, "onAccessibilityEvent");
        String text = event.getText().toString();
        Log.d(TAG, text);
        }
    }

    @Override
    public void onInterrupt() {

    }

    @Override
    protected void onServiceConnected() {
        super.onServiceConnected();
        Log.d(TAG, "onServiceConnected");
        AccessibilityServiceInfo info = new AccessibilityServiceInfo();
        info.flags = AccessibilityServiceInfo.DEFAULT;
        info.packageNames = new String[]{"com.android.phone"};
        info.eventTypes = AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED;
        info.feedbackType = AccessibilityServiceInfo.FEEDBACK_GENERIC;
        setServiceInfo(info);
    }
}

AndroidManifest.xml :

<service android:name=".services.USSDService"
                android:permission="android.permission.BIND_ACCESSIBILITY_SERVICE">
    <intent-filter>
        <action android:name="android.accessibilityservice.AccessibilityService" />
    </intent-filter>
    <meta-data android:name="android.accessibilityservice"
                    android:resource="@xml/config_service" /> // created below
</service>

res/xml/config_service.xml :

<?xml version="1.0" encoding="utf-8"?>
<accessibility-service xmlns:android="http://schemas.android.com/apk/res/android"
    android:accessibilityEventTypes="typeAllMask"
    android:accessibilityFeedbackType="feedbackSpoken"
    android:accessibilityFlags="flagDefault"
    android:canRetrieveWindowContent="true"
    android:description="@string/accessibility_description"
    android:notificationTimeout="100"
    android:packageNames="com.cootf.sims"
    android:settingsActivity="com.example.android.accessibility.ServiceSettingsActivity" />

Run the code --> Enable the accessibility through Settings --> Accessibility --> [Your app name] --> Enable. Job Done!

USSD is not yet supported on Android. There is a feature request for it: http://code.google.com/p/android/issues/detail?id=1285