I was the head tech for a autodialer company many years ago. To answer your question It is against the law, it has always been against the law since the early 90's, it is legal for some non profit and for political campaigns, but they must also use a DNC list. As stated before if you have an existing business relationship with someone you can contact them via automated dialer.
If this is what you want to do then, just be careful, make sure you use a DNC list, you will still get complaints, just not as many. Don't give out your personal info in the broadcast. If you want to use a number just use a free voice mail service. If you own a carpet cleaning service just say we are running a special today, and you will have people leaving their name, most will tell you to f-off, add them to your DNC and move on.
Just so you know 50 to 60% of the numbers on your list will be on the DNC list, but if you have good software it should skip those numbers pretty quickly.
I also know someone that still dials and does not use the DNC he blocks his analog line(*67) then at the end of the day if he get's 10 leads, he just checks the leads against the DNC list, if they are there he doesn't call them back.