It's a matter of backup for Power Outage. In addition, when I use broadband, I notice more mischief than on dial-up. So I asked in the Home Address IE box about the reason for using dial-up. I was pleasantly surprised with this response at the top of the google listing from the POV of alarm systems.
PEPCO advises dial-up as backup (AT&T Princess type phone) for power outage. I've used it at midnight when even the police couldn't get AT&T. It made me feel secure. Especially since the utility is part of my condo fee. Not all parts of this community were effected. However, the PEPCO person who answered my phone did put my number in their robotic database to verify that the power was restored. The Website said it would be fixed by 8am. The robot woke me up at 5am and I was so happy to be cared for and pushed "1" to ack all is OK. You can't imagine at midnight, looking at TV, working on my PC and it's dark suddenly all around. No one knew. I got my AT&T Princess (always kept up dial-up but had those answering machine type phone) when my daughter who works in Houston told me she had to get one to do business under the same scenario. She found someone who had an old POTS AT&T phone.
This article helped me keep up-to-date. I only use dial-up for voice communications and hardly ever use it. I use email for communications, even for making appointments for phone calls. I stopped paying for caller ID. I screen all calls. I'm 83YO and a stay at home and grateful I can. I use broadband all the time but do budget for dial-up as backup. Even with out the problem of power outage, because people can spy on me, when buying my home two years ago I was forced to go dial-up and scanning and sending documents that way. It seems to be T-1 connection. I don't know why we all in the USA can't simply have a T-1 connection. I think parallel to this that the USPS should be able to maintain an email address data base for every one in the USA. I consider posting this message the same as email. Especially since mobile phones can read and send email.
Anyway here's what I just read and it says I'm budgeting wisely for my own security. I think of all communities under Boards of Directors should have a PBX dial-up. I don't know about costing this out though. Sometimes security overrides speed. Also lower speed forces patience and more logical thinking.
Alarms and Phone Lines FAQ