As long as you have an Alarm.com compatible panel with an unregistered cellular module (4G LTE) you can get started with service. If your module is not unregistered, talk to your previous service provider as they can assist. Typically the cellular module is unregistered during account cancellation.
A list of compatible panels can be found here:
Steps on how to find your 15-digi IMEI can be found here:
You can use this tool the check if your module is unregistered:
I it is, you can begin the service plan purchase process here: