This is what they have on their site if you try to signup. (Only spoilered for length.)
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Use a phone to verify your account
The phone number you use can only verify one account. Once you enter your number, you’ll receive a code that you can enter on Facebook to verify your account.
Your phone number will be added to your Timeline. You’ll be able to choose who you share it with. To learn more about how information on your Timeline is used, visit our privacy policy.
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Confirm Your Identity
Having trouble?
If you’re unable to verify your account using a mobile phone number, you can submit a request to verify your account using your ID.
Why do I need to verify my identity by providing my phone number?
We want to make sure that this is really you and that you’re connecting to Facebook with just one account.
To verify your identity, you’ll need to log into Facebook and follow the on-site instructions to add your mobile number. Your phone number will be added to your profile, but you can choose who can see it there.
Note: Maintaining more than one account is a violation of the Facebook Terms.
Maintain an authentic personal account.
Do I have to use my name when I’m using my Facebook account to access games and apps?
If I use my phone number to verify my identity, will it appear on my profile?
Why can’t I use my phone number to verify multiple accounts?
I can’t use my phone number to verify my account.
If you’re unable to verify your account using a mobile phone number, you can submit a request to verify your account using your government-issued ID.
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Confirm Your Identity
Please fill out the form below to help us verify your identity.
Please attach a copy of your ID(s). Learn more about why we require ID verification and what types of ID we’ll accept below.
What types of ID does Facebook accept?
You can confirm your identity in 1 of 3 ways. When submitting documentation, please cover up any personal information we don’t need to verify your identity (ex: credit card number, Social Security number). We encrypt people’s connections to Facebook by default, including IDs you send to us. We delete your ID information after verification is complete.
Option 1
We will accept any government-issued ID that contains your name and date of birth. Examples include:
Birth certificate
Driver’s license
Passport
Marriage certificate
Official name change paperwork
Personal or vehicle insurance card
Non-driver’s government ID (ex: disability, SNAP card, national ID card)
Green card, residence permit or immigration papers
Tribal identification or status card
Voter ID card
Option 2
You can provide two different forms of ID from the following list (ex: a bank statement and a library card, but not two bank statements). The names on your IDs must match each other, and one of the IDs must include a photo or date of birth that matches the information on your profile.
Below are some examples of IDs we’ll accept:
Bank statement
Bus card
Check
Credit card
Employment verification
Library card
Mail
Magazine subscription stub
Medical record
Membership ID (ex: pension card, union membership, work ID, professional ID)
Paycheck stub
Permit
School card
School record
Social Security card
Utility bill
Yearbook photo (actual scan or photograph of the page in your yearbook)
Option 3
If you don’t have an ID that shows your authentic name as well as your photo or date of birth, you can provide two forms of ID from Option 2 above, and then provide a government ID that includes a date of birth or photo that matches the information on your profile. We won’t add the name or other information from the government ID to your account.
How do I upload my ID to Facebook?
Why am I being asked to upload an ID?
We take your security very seriously, so before we can provide you with any information about this account or give you access to it, we need to make sure it belongs to you.
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