I am reading the other responses that are here, and so far they have missed the mark.
The recruiters you are speaking to are not out to scam you when they mention four digits of your Social Security number. They're asking for these four numbers because when they submit your information, they need something that uniquely identifies you to prevent dual submissions to an end client. If an end client receives your information twice for the same position, it will reject both applications because there are legal implications that arise should two recruiting companies argue over who submitted your information first.
That said, make up a four digit number that is different from your SSN. Always give the recruiters this same number. They don't care. It just needs to be unique. Should the situation progress through interviews to a real job, put your real SSN on I-9 and W-4 forms. So we have solved this problem.
A second thing to realize is that many of the recruiters are paid what would be a very low wage in the US, and are working from offshore. Because of VoIP technology, you would not know immediately that they are offshore but I have noticed over the years a trend for the companies to use phone numbers linked to New Jersey. If you are interested in a job, ignore the New Jersey thing. When you speak to recruiters, ask if they are filling jobs for their direct clients. This is important. Contract jobs are okay, but you really don't want to work for a contract firm who has been hired by another contract firm who has been hired by yet another contract firm that has been, finally, hired by the company paying the bills. Avoid these sorts of situations like the plague, because the wages you make have been 'stepped on' several times before they get to you, and you will almost always be offered a rate lower than Market for your services.
If you have a problem with someone's accent, and can't understand them, request that a written job description be sent to your email. The people who make the initial phone calls really don't need to speak The King's English, and if you decide to pursue things further you will be in touch with an account manager whose English will definitely be better. This is annoying, but this is how the hierarchy works.
Best of luck.