So the 2-tone you hear at Sky Harbor is not for FS19 nor FS29. Its a minitor pager that sits on a console within the Sky Harbor Comm Center. It notifies Sky Comm of Fire's response to any airport incidents. Its done automatically with Samantha and sets off the pager for any incidents within a predetermined footprint around Sky.
Its a little funny when it goes off for Central City calls at the washington street light rail station.
TOL BC161 and a few other BC's have 2-tone pagers. Gila Bend Rescue also had one when they were dispatched by PFDRDC.
Everything else is done through the Phoenix G2 station alerting system (there are some videos on youtube describing this).
So that would explain the 2 tones prior to the standard tone on A1 for station 19 then. Knew about the G2 system. Speaking of tones, I really wish they would use tone signalling instead of patching the analog tone over digital. Although, it does provide for some humor when it goes out and it sounds like it's whining and complaining about abdominal pains.
So after a bit of monitoring and logging, here is what I have so far. Please correct me if I've got this all wrong:
Mesa Fire B1
645.1 translated into 645.7
And for SWA, I have a couple:
601.2 translated into 602.6
606.3 translated into 607.5
569.1 - seemingly matched to 569.1
Haven't heard any two-tone on SWA as of yet.