but the stupidest thing I have ever seen it that cell user have to pay for
incoming calls and 800s numbers
You're paying for airtime -- the convenience of having a phone not hard-wired to the wall; a phone that can be used anywhere, and receive calls anywhere. Airtime costs no matter who originated the call; it therefore makes sense to charge for it either way. Many of us have phones that don't charge for the first minute of an incoming call, so if it's a wrong number you can get rid of him and it doesn't count against your airtime allowance.
