I'm trying to park a landline number but NumberBarn's site is asking for a mobile account number and PIN.

In this article:

While account numbers and PINs are required to successfully port in a mobile/wireless (cell phone) number, that information isn't required to port in a landline/wireline (home or office phone) number.

Rarely, our system may still ask you for that information if it mistakes your wireline for a wireless number. Just enter a placeholder like "1234" in each field. Then, before you authorize the port-in request:

• Click on the "Numbers" tab in your account.
• Click on the number you are porting in.
• Click on the "EDIT ORDER" button:
• Erase the placeholder account number and PIN you submitted.
• Click the green "Save Updates" button to save your updates.