Interactive Intelligences has been performing SIP interoprability testing for many years now. We have tested IP Phones and gateways from many different vendors over the years. We have seen significant growth in the maturity of the SIP from these vendors as well as in our own SIP stacks. Today as new products from new vendors arrive to be tested in our lab the testing cycle is typically much shorter than it was just a couple years ago. Even just a couple years ago we could end up going through multiple firmware releases from a vendor to correct interoprability issues found in our lab. Today the testing cycles are shorter. Knowledge of SIP and common interpretations of the standards is growing and maturing.
Perhaps one day soon SIP validation will be a very quick and simple check. Resellers will see that a new SIP device and have confidence that it will work with their IP PBX.