Its been awhile since i played with alarms, but I suspect you will need the installer code, as that's required to access the programming function, then these instructions www.paradox.com/Downloader/?T=URL&URL...EI09.PDF and go to section 8.1 to disable the dialer.

If this was installed by a professional company, then you may need to contact them, as often only they have the installer code. (until you got ride of your landline, they may have even been able to do it remotely).