capture messages returned by USSD code

How can I capture the message returned by the execution of a USSD code on android, for later use within an app? the call I do it by means of a button (in the onClick) already with its permissions and everything what the activity takes:

...
      Intent iDatos=new   
        Intent("android.intent.action.CALL");      
      iDatos.setData(Uri.parse("tel:*222*328%23")); 
      startActivity(iDatos); 
... 

There, everything runs fine. there is no problem Execute the USSD code and return the following message: "You have 4.9 MB valid for 17 days For a new purchase dial * 133 #" Problem: How can I save that message and then decode it in parts and save it? For example: the available megas: 4.9 MB