The SCARIEST thing about those kind of scams is that they would just go away if they were not having success at getting someone to fall for them. Kind of like being told you won a lottery you didn't enter. You have to really TRY HARD in order to make yourself believe that kind of stuff :)
Cell phones, especially mine, get near ZERO junk calls. And they have this magic device called a 'screen', which displays the number of the caller
BUT there are SO many ways for them to block their number from appearing that it's a worthless system. Better strategy is to just not answer ANY call that blocks their identity from you.