I created an account with a fake name and mailinator email (after several tries where it rejected mailinator domains, it finally worked with bobmail.info). It asked me for my cell phone number to confirm, and when I entered the code it had quite a large number of "John Doe is someone you may know". These people are not all people who I'd expect to have my phone number saved in their phones. My phone number is linked to my primary account, but I don't think it is visible.
1) Apparently my cell phone number used to be registered to my primary account. When I created the fake account, it removed my number from my primary account and assigned it to the fake account. So what happened there was they suggested friends from the account that used to have the same phone number assigned to it. The creepy thing here is that it also suggested people that I had recently defriended.
2) I did the same thing, using my Google voice number which had not previously been registered to any FB account, and was suggested three friends who apparently have me saved in their address books.