I have just replied to J Connor with this same information.
You need an EIN number.
If you have an iTunes Connect account, open it, check out the Banking and Contracts section.
You can open and walk through the forms and make notes of what you need.
I have a UK account and it requires an IBAN number from your bank. If you have online banking, email/ message a request or walk in your branch and ask for one.
If you phone the USA...get a phone card which allows low cost calls.. IT TAKE UP TO 15 minutes to go through the application...and they give you the number , although Apple will not see it foe at least two weeks... they send old fashioned letters to you and Apple!
Ignore all the hard luck stories, its a simple process, download the SS4 form from their website, print it, fill it in, they will ask if you have it.
Any problems get back and they can be redolved