I went to school just as v9 was released, we actually upgraded the classroom systems from 8 to 9 as I were there the week it released... I wanna say that was fall of 2008. At that time the 3300 school was two weeks long in Phoenix, and 9.0 released the day we started the class. Although by this time I had been working on the 3300 for several years, I can remember working on releases 4 and 5 and even a few 3's, they were quite finicky back in the day when the SX-2000 was Mitel's flagship PBX.
Sip trunking support was released in the general release of 7.0 in April 2006, there was no SIP trunking support prior to this release. SIP phones were supported from the initial release 3.0 in 2001.
The attached document should tell you what your looking for though...