The basic 7 digit number is generally like this:
Read the first 3 numbers as single digits, and the last four as two double digit numbers.
525-2793 is read, "Five two five, twenty-seven ninety-three."
A single zero is read as letter O.
525-2703 is read, "Five two five, twenty-seven oh nine."
2 zeroes in final position make a "hundred".
525-2700 is read, "Five two five, twenty-seven hundred."
3 zeroes in final position make a "thousand".
525-5000 is read, "Five two five, five thousand."
888-5555 could be read,"Eight eight eight, fifty-five fifty-five." or "Triple eight, fifty-five fifty-five."
In noisy conditions it's best to resort to reading each digit separately. And, this last method is correct in every case, noisy or not.
929-4501 "Nine, two, nine, four, five, zero, one."