How did they get my number? (T-Mobile, opera, cellphone, price)

[Eeyore1]

A few months ago, I switched to a T-Mobile prepaid cellphone. I have been really happy with the phone and the price. I've given my phone number out to family, employers, utility companies, doctor's office, etc. I have not given this number out to anyone unless it is on a "need to know" basis.

One thing bothers me, though. Why is it that I get calls from telemarketers? How did they get this number? The number is on the "Do Not Call" registry, but I don't know if that makes any difference.

[Asheville Native]

The 'war dial' simply dialing every number in consecutive order. Their equipment senses if someone answers and it tries to switch to one of their live operators for the pitch.

Or someone else had that number before you did.