That was my plan, as well, and the plan failed.
First, the range on the CM15A leaves a lot to be desired. Even with an antenna modification, I had a 50/50 chance of missing signals from the sensors at the edge of my effective range (in a 1700 square foot house). I basically would go out through the garage, lock the door, and then walk around to a window to arm the system, since that was the "sweet spot" for the CM15A to pick it up.
Also, I'd often get blank messages from onAlert, which made me stop whatever I was doing and go home to make sure nothing had been triggered.
I like the console. I like the remotes and I even like the power horns (for indoor sirens, anyway). I like the fact that the wireless door/window sensors are less than $4 each when you buy them in a good deal from X10. They have a lot of uses, not just for your burglar alarm, as long as you can receive their signals.
Like Jytkal, I wrote my own software. Actually, I bought a V572RF32, disabled the CM15A's RF daughterboard, and THEN wrote my own alarm software. It is a big improvement over the old setup, but it does have its limitations. The software still requires the use of a CM15A, to receive powerline signals from the V572RF32.
The next version is going to use the W800RF32A to receive all signals directly, and will use a CM11A, but only for sending commands to devices (lights and sirens).
I monitor the heartbeat signals full time in my app, mainly because I'm writing a function to let me know that I should check the batteries if I go too long without getting an update from a sensor.
Here's a screencap of what the little crapplication looks like