No, the thermostats could not be used with a new account.
Alarm.com has ended support going forward for these discontinued models because they are discontinued and missing capabilities necessary for upcoming thermostat features through ADC. This applies to all new accounts.
You may continue using any of these thermostats on accounts created prior to 5/20/2018.
If you cancel service and resubscribe or if your service is suspended due to overdue payment and you later sign back up for service, unfortunately the CT100, CT30, and GE TSTAT-300 cannot be used remotely through Alarm.com.