When you first got the ATA, it wasn't configured automatically at bootup or after a factory reset.
It needs to be entered. I don't know how it's entered since I don't work for Fongo, but I speculate something, such as the following, happens:In other words, does the MAC address have to be manually entered
When you purchased the Grandstream HT-801 from Fongo, the MAC address would typically be entered in the provisioning system before the ATA ships to you. Or there could be a bunch of HT-801 MAC addresses entered already (I don't know if Fongo has bulk quantities of HT-801s already. Maybe not), but none are authorized for activation until after shipment occurs. Regardless, the MAC address needs to be entered (it could be an automated process, but it's not done on your end) first.
This means Fongo is supposed to have already associated that particular ATA's MAC address with your Fongo Home Phone customer account before you plug the ATA in. Then when you receive the device and plug it in, the ATA will connect, sending its MAC address, to the provisioning server, and obviously your WAN IP address is now known to the server since your IP is being used to the send the request. Since the provisioning server already has (or is supposed to have) your ATA's MAC address linked to your Fongo Home Phone account, the provisioning server accepts the request and configures your ATA. There may be an additional authentication process that I'm unaware of as well, and it's also possible that the ATA's firmware version needs to match one that is approved by Fongo before configuration is permitted.
The automatic recognition of the MAC address is part of the provisioning process, but this assumes that the MAC address is already registered in the system at the time your ATA is connected to the internet and boots up for the first time.
If you want to know what happens precisely, it would be advisable to ask Fongo via a ticket instead of me, because other than what I've already expressed, I'll just be speculating, uselessly. Not only am I not a Fongo Home Phone customer and unable to observe what's happening, I'm also not a Fongo employee.