There are 720 different combinations for a seven-digit number. This answer can be found using the (n[n-1][[n-2] ... to k factors)/k!, where n is the possible number of digits and k is the number of digits in the number. For a seven-digit number, the formula is 10!/7!.
In math, an exclamation point following a number indicates a factorial, meaning that the number is multiplied by all of the positive integers less than itself but not including zero. For example, 10! = 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 = 3,628,800. A combination does not consider the order of the digits.