That could be an option as monitored alarms can't work with quite a few plans.
I think the site needs to provide a link to information about this problem and not say you can't use the products, because that's not true.
I have a monitored alarm.
I moved to VoIP and just had to make some changes to my alarm system and the monitoring.
I got better service in the end and pay less for it.
Yes - this simply won't be possible with some systems and some companies, but that should not exclude the retail offering of that ISP. It just means we need to provide a bit more education to the user.