Right, I wouldn't worry about the SIP support in general, it's only the OpenStage 80 hardware that was discontinued. (Actually already in late 2012, not 2013 as I remembered.)
So it would seem that 2 years after discontinuing the product, Siemens has decided to stop providing software updates for it. Which is understandable, but kind of sad, considering it's pretty much the same hardware as the OS 60, just with a different screen and case. Oh well. :\