In the US, there is actually a lot of legislation that protects people from such annoyances. For example, if you are on the National Do Not Call List then telemarketers are not allowed to call you. They will still call anyway on occasion, "by accident". You can then ask them to take you off the list, and they will usually comply. Unfortunately you will have to repeat this for each company. If any individual company persists in calling you despite being on the DNC and telling them no, record the calls and find a lawyer. You can probably sue and win.
However this doesn't help with non-US companies or criminals. I think these days it goes like this:
- A company pays a telemarketer in India to advertise
- Telemarketer purchases list of phone numbers on the internet
- Telemarketer registers a SIP account with a US forwarder, or purchases a hacked account
- He starts calling people like you
- US government hears about it and investigates
- They find the forwarder, tell them the account is being used for illegal marketing
- Forwarder says "Oh no, those awful telemarketers! Thanks for letting us know, we'll close his account right now!"
- By then the telemarketer has already called a bunch of people, when the account dies he just goes back to step 3 and repeats
While the government is playing this whack-a-mole with them you still get called many times.
is it legal for them to call me at any time of the day or night
No, usually unsolicited calls late at night can be considered harassment. Unfortunately in such circumstances best you can do is have the authorities compel that telemarketer to not call you again, but it doesn't mean other telemarketers can't call you. However, many jurisdictions have specific laws restricting telemarketing calls as well.
are there risks to have one's info exposed in such a way
Of course, one is that your phone number will be harvested and sold to spammers, another is risk of identity theft.
The extra fee to hide your info is not a terrible idea, but keep in mind that the hoster will probably sell your info to advertisers anyway. The concealment will at least prevent small time spammers from harvesting your number without paying for it.
are there things I can tell the caller to make them stop calling... forever?
Not for those illegally calling. They already know it's illegal, but they have figured out a way to get away with it.
One thing you can do is not pick up, or pick up but not say anything. That might make them mark your number as automated or invalid in their list. But they wouldn't necessarily tell other telemarketers that your number is invalid.
What would be the risks of acting in a hostile manner to the callers?
Hardly any. Might be better to avoid saying anything illegal, like threats, but the person is probably not subject to your jurisdiction so even that is unlikely to have any consequence. Some of them threaten to put you on all the lists and call you hundreds of times every day as revenge, but that's unlikely: They get paid to attract paying customers (most of them are actually looking for very stupid, gullible people), calling a number they know isn't interested is a waste of time and money. As for calling you repeatedly, if the same person or entity calls you again and again you can easily go to a lawyer and sue, so they wouldn't do it.
Attempting to take legal action against random telemarketers has no risk in the colloquial sense, but it has a huge risk in the financial sense, because you'd waste a bunch of money in lawyer fees trying to sue some guy on the other side of the planet. These guys already have the FBI and others trying to track them down, there's not much you can do on your own to stop them.
if I take action to block all unknown numbers with my service provider, am I liable for not being reachable?
Yes, but these days it is surprisingly rare to get unexpected legitimate calls. All your friends are already in your phone book, any important companies like your bank can also be added, but they will typically not only call you but also send you emails or paper mail. Generally very few companies will only call your number and give up - people change or lose numbers all the time, or are not able to pickup, so almost everybody knows that phone numbers alone are not a reliable way of contacting someone. There are also various apps for your phone that try to detect and block known telemarketers, which is a less drastic option.
The best idea here is to avoid giving your number to untrustworthy companies to begin with. Even if the company is legitimate (like a store) they could sell their database, or have it hacked. Because it is now fashionable for many companies to require a phone number for their service (using the numbers for marketing is a huge revenue source so of course they require it) your best bet is to have multiple numbers. Have an "important" number that you actually use, and give out to people you know personally and reliable companies or government agencies that have a reason to call you. The other number can be given for all those idiotic stores that demand your phone number for some trivial transaction - give them the decoy number and then ignore calls to that (except for things like confirmation SMSes).