bsotak, welcome to Ooma. You're right that Ooma's official stance is that Ooma doesn't support alarm systems.
However, that doesn't mean you can't try and see.
Since you mention that your alarm worked with other VoIP, does that mean your house wiring is setup in a way that your VoIP has worked with alarm line seizure? You can tell if your setup works with line seizure by looking at your call logs. If testing alarm call out creates call log entry, your wiring setup works with line seizure. If no entries in call log, your setup doesn't work with line seizure.
In case your setup isn't right, let's talk about alarm line seizure and how to make Ooma work with that first.
When alarm calls out, it cuts off dialtone access to every walljack (line seizure) so phones connected won't be able to disrupt the alarm call out. If one is to simply feed VoIP dialtone to a walljack, line siezure would cut off the very dailtone that alarm panel needs so no call out can happen.
One has to make sure VoIP dialtone gets fed to a point upstream to the alarm panel. One way is to get the VoIP dialtone to the NIB via the 2nd pair and then have the dialtone come in the house on the first pair as if the dialtone was coming from the phone company.
First, make sure house wiring is disconnected from the phone company by unplugging the plug in the NIB.
If you have the swing door type NIB, you'd need to get your wires off the screws.
At a walljack near your Ooma device, plug in ones of these L1, L2 Splitters
Feed your Ooma dialtone ("Phone" port) to L2 of the splitter.
At the NIB, connect the 1st pair & 2nd pair.
If the plug type NIB, just connect the orange wire to the same screw blue wire is connected to and connect the white orange to the same screw white blue wire is connected to.
If you have one of the swing door NIB, get the wires off the screws and connect blue and orange together, white/blue & white/orange together using these phone wire butt connectors:
After doing this, your setup should work with alarm line seizure; you'll be able to see call log entries when you do alarm call out tests. From this point on, it is a matter of whether you can get a successful handshake with alarm central or not.
As for programming your alarm panel for dialing prefix and such, I don't use *99 but rather *70 (disable call waiting)
viewtopic.php?t=9637#p66843
If you have a Telo, you can try *98 prefix as well to see if that works better for you.
As far as programming the ADT panel to add dialing prefix, check this out:
http://forum.doityourself.com/electroni ... l-out.html
Read the FAQ here for much info:
http://forum.doityourself.com/electroni ... sting.html
Also check out my experience with *99; ended up using *70 for best results on my panel:
viewtopic.php?t=8957#p62487