the OK button calls only if the line has a non-empty buffer

src/gui/official/PhoneLine.cpp

@@ -102,8 +102,10 @@ PhoneLine::sendKey(Qt::Key c)
 void
 PhoneLine::call()
 {
+  if(mBuffer.size()) {
     call(mBuffer);
   }
+}
 
 void 
 PhoneLine::call(const std::string &to)