Take the imaginary telephone number 12345678910. Americans write their telephone numbers like this: 1-234-567-8910. The 1 is only used when you are dialing another area code within North America.
When you pronounce it, you break with the hyphens. You would say: One. (Pause) Two three four. (Pause) Five six seven. (Pause) Eight nine one zero (zero is also pronounced "oh"). Some might combine the last four digits to "eighty nine ten."
Not a teacher, by the way.