The total amount of numbers that can be made is equal to the product of the amount of options for each digit.
The first digit has only 6 options: 1, 2, 3, 4, 5, or 6.
The other six digits have 10 options: 0,1,2,...,9.
Then, the total amount of different telephone numbers is six million:
[tex]6\times10\times10\times10\times10\times10\times10=6,000,000[/tex]