There are 900 possible three-digit numbers not beginning with 0. (Note, however, that this question does not accurately describe the restrictions on numbers that can be used as area codes.)
With 123 digits you can make 123 one-digit numbers.
12 numbers
Not sure what a "didget" is. It is possible to make 18 5-digit numbers.
As far as I can tell, all 5 digit numbers are potential zip codes, so there are 99999 + 1 potential zip codes, or 100,000. Many of these are not actually is use.
8
720 of them.
162
5040
6, as long as they are all different
You could just keep typing random numbers. Make sure it is a 10 digit number because that is how many characters the code has in it. I hope I helped!
8*10*10=800