The default credentials are as follows:
»
192.168.2.4/admin/advancedUsername: admin
Password: [nothing]
If that doesn't work, and the model number is actually PAP2-NA, you can factory reset it. Connect a phone to the ATA and dial ****73738#. After doing this, the credentials I posted should work.
Note that you will need to turn off Caps Lock to make this work properly. (Also you should turn it off when posting here.)