This could be done in any lab with a few voip gateways, but why? If properly designed this should not happen even in a Service provider environment where various IXCs are involved. VoIP only came about because of toll arbitrage. If I have sent it the brunt of its distance for delivery I should be close enough to the user not to cause a tandem encoding scenario. I guess the issue could come in when a call is originated by an enterprise voip deployment then sent to traditional pstn which uses an ITSP(internet telephony service provider) to carry its traffic back to a VoIP enterprise environment. BUT the enterprise voip environment should be using G711 on campus, and the issue should be moot again.