Uhhh, nope. *Selling a call and buying a put is either a collar or creating s short term bond, depending on whether the strike prices are different or equal.
I haven't looked at Gateway's procedures.Thinking about it, they probably but not necessarily are doing covered calls and protective puts. What I said is true in essence if there is no underlying stock. Clearly, it wouldn't exactly mimic a short because of variations in strike etc.- but one's profit-risk graph in each case would show unlimited upside risk above the call strike, with the downside captured south of the put strike. And I suppose I should also say that while a short sale of stock is theoretically open-ended as to time, of course the options are not. Plus blah, blah, blah.
You are corect that by definiton the same option position where the call sold and the put bought are matched by a long stockholding is called a collar, if certain conditions are met.
I am not sure how knowing that helps the original poster answer his question which was "can this be approximated with stocks and bonds".