Pseudorandom telephone generator
Assuming you're looking for numbers of the format XXX-XXX-XXXX (keeping in mind that this excludes international numbers):

I wouldn't separate the printing onto separate lines. I would build up the number (perhaps extracting this logic into a function) and then print the whole thing. You can also eliminate those unnecessary loops by generating numbers in different ranges and using different formatting strings to add the leading zeros (ex. a routing code of 2 should be 002).

You'll also probably want to handle the case that an invalid area code is input. For this, I pulled out the prompt into a separate function that can be used in a loop (until a valid area code is given).

Finally, for scripts you should wrap the main action in if __name__ == '__main__':

#!/bin/env python3
from random import randint


def random_phone_number(area_code):
    """Returns a random phone number (XXX-XXX-XXXX) with a given
    area_code."""
    prefix = randint(0, 999)
    line_number = randint(0, 9999)
    return f'{area_code:03d}-{prefix:03d}-{line_number:04d}'


def prompt_area_code():
   """Interactively prompts the user for an area code, returning it."""
   while True:
       try:
           area_code = int(input('enter an area code: '))
       except ValueError:
           pass

       if 0 &lt;= area_code &lt;= 999:
           return area_code


def main():
    print(random_phone_number(prompt_area_code()))


if __name__ == '__main__':
    main()


Things of note:


f-strings (new in Python 3.6)
Handling exceptions
int converts a string to an integer or raises a ValueError