Do you put in the area code when calling a mobile from overseas?

That depends. If you are calling a mobile phone with a Fresno number, from a landline in Fresno, you can dial just the 7-digit number. If the mobile phone has a different area code, you will almost always need to dial it, and in many states if the mobile phone is not a local number for you, you may need to dial the area code, even if it's the same as your own.