Thanks for coming back to me @Gesmond, this may also be a question that needs to be placed towards the alarm company.
But you should be able to plug in the service via the 2nd Telco port on the back of the hub - you may however need to purchase an adapter to accommodate for this - which may be an RJ11, but the alarm company should be able to confirm this for you.
The actual switching over, from landline to VoIP, would as far as I'm aware be the very configuration you're referring to.
Kindest regards,
David_Bn