It is illegal for telemarketers to knowingly place a call to a wireless number using any automated dialing system or pre-recorded voice message unless they have express prior consent. Now, you can give that consent via a proxy, such as if it's in the terms and conditions with an affiliated partner, but in general, all you have to do if you receive an automated call is to speak to an agent, let them know it is a cell phone and that you do not consent to any contact attempts to that number. You can also register your number on the do not call registry, but many cell phone numbers are "scrubbed" through a database that identifies them as probable land-lines or cell phones. Repeat violators should be reported to the FCC at this link:
https://consumercomplaints.fcc.gov/hc/en-us/requests/new?ticket_form_id=39744
Most all spam is illegal to phone lines if the number is on the DNC list. (There are exceptions for political calls, charities, someone you've done business with and have a relationship with.)
The problem is that legality issues do not stop the spammers. The people selling mortages, selling home alarm systems, running IRS or Microsoft scams, offering to reduce interest rates....They don't care and the FTC does not have the resources to stop them.
These are disreputable companies per se. Many if not most of them have been accused of scams, not just spam, but when you have companies deliberately engaged in massive violations of law, consider them disreputable per se. DO BUSINESS WITH NONE OF THEM. Legit companies do not act this way:
1) They don't violate the do not call list; (illegal) (and if they are calling you with robo calls, they are probably making 10s of thousands of them---massive violations)
2) They don't dishonor personal requests not to be called again (illegal)
3) They don't give you phony Caller id notes (illegal)
4) They won't give you identifying info on their company--failing to identify oneself is illegal
5) They won't give you a callback # (see #4)
So, when it goes something like this, run for hills (the "Q" is from the consumer; the A from the scammer)
Q. What company are you calling from?
A. Credit Card Services
Q. Yes, but what company?
A. Credit Card Services.
Q. What's your address?
A. We don't give that out?
Q. What's your website address?
A. We don't give that out until you've given us your credit card and we determine you qualify
Q. Nice scam
A. You are a *$#U%@)(U% sir, you're useless and you know nothing.
A year or so back there was a huge class action lawsuit against one of the key spammers they caught in Florida. For a few months, my phone lines were actually cleaned up! No calls. Then, it started again. They just put up another phony call center and the robo calls begin again.