Your code does not match the Java equivalent that has been sent to you. This is the equivalent:
uses
Androidapi.JNI.GraphicsContentViewText, Androidapi.JNI.Net, Androidapi.Helpers;
procedure TForm1.Button1Click(Sender: TObject);
var
MobileNumber: string;
Intent: JIntent;
begin
MobileNumber := '*155#';
Intent := TJIntent.JavaClass.init(TJIntent.JavaClass.ACTION_CALL);
Intent.putExtra(StringToJString('com.android.phone.extra.slot'), 1);
Intent.putExtra(StringToJString('simSlot'), 1);
Intent.setData(TJnet_Uri.JavaClass.parse(StringtoJString('tel:' + MobileNumber)));
TAndroidHelper.Context.startActivity(Intent);
end;
I don't have a dual SIM device to test this.
Those are not equivalent. TJIntent.JavaClass.EXTRA_PHONE_NUMBER is "android.intent.extra.PHONE_NUMBER", not "com.android.phone.extra.slot"