Here are a few things to consider. Do some research - don't post details, but do look for patterns...
What kind of phone switch?
What kind of phone?
Does the phone currently have an extension?
What is the main site number?
What number does the most important person have?
What number does a wall phone have?
Does the fax machine have a number in sequence with the main line, important person or wall phone?
Can you dial other "remote" sites by an extension?
If your site goes down, does the remote site loose their phone system?
Do you dial 9 to get an outside line or press a special button?
If you were to ask an employee, how do I call you from my cell phone, would they tell you:
a. "dial xxx-yyyy"
b. " dial xxx-yyyy and tell susan to call me"
c. "dial xxx-yyyy and press 1, then enter my four digit extension"
d. haha "Your not my type"