Get with the program, VMS manufacturers. Develop SIP communication software drivers or get left behind. Seriously, is it really that hard?
Ok, that was kind of a side note. As to the horn itself, not a bad little device. I think it's competitive to some combinations I have seen with horns attached to self amplified POE SIP devices from various intercom and VoIP brands. Kudos to Axis to be smart enough to make it SIP compatible and not just API only requiring a specific software driver being developed.