I'm not sure if I can address your specifics, but what I have found is that the success or failure of adding commas depends on the phone system to which you are calling. Some systems require the "+"; but in those that take a comma, the comma represents a pause. How long should the pause be? That is, how many commas? Depends on the phone system. Some respond immediately, others require the outgoing instructions (e.g., if you know your party's extension, enter…") to completely end. Annoying, but if you listen and try varying amounts of commas (yes, requires repeated calling), eventually something should work.
