You can sign up for an account with Pearson Vue but can't register for the exam without the ATT.
From Pearson Vue Website:
"AUTHORIZATION TO TEST (ATT)
After your board of nursing declares you eligible, you will receive your ATT Letter.
Note: You must have your ATT letter to schedule an appointment to take the NCLEX and you must present your ATT letter at the test center on the day of your examination to be admitted. You will not be admitted to the examination without your ATT letter and will be required to reregister and repay to take the examination.
• The ATT letter contains your authorization number, candidate identification number and an expiration date.
• TheATTletterisvalidforaperiodoftimespecifiedbytheb oardofnursing(variesfrom60daysto365days;however,th eaverage length of an ATT is 90 days).
• Once the board of nursing declares you eligible to test and your ATT letter is issued, you must test within the validity dates of your ATT letter.
• The ATT validity dates cannot be extended for any reason. If you do not test within these dates you will have to reregister and repay the examination fee."