@anon226359: The way these scammers get your cell phone is not because you've necessarily given it or posted it. They have dialing machines that go through numbers in sequence. For example: 555-0000; 555-0001; 555-0002; 555-0003, and so on. So, they're bound to hit on a legitimate cell phone number sooner or later.
But you're right: it's a scam and no one should pay any attention to this or to similar e-mails.
However, residents of the USA can report these texts and e-mails to the Federal Communications Commission online so a record can be started for these numbers. USA residents can also have their cell and home numbers put on a Do Not Call list so that, if a telemarketer does call, then they are in violation of federal US law.
But the way they get the numbers is usually through a sequential numbers dialing program. However, your cell phone company may also be able to block calls from a particular number, so it may be worth checking into.