we went to Letsencrypt site, and found the root cert pem file which we placed on our TFTP server and typed the pem file name into the GUI on the phone - down the left hand side of the GUI is TLS Support
Root and Intermediate Certificates Filename - this is where we typed the pem file name
we can see from the TFTP logs that the Aastra 67xx phones have downloaded the pem file but get a 508 registration error in the "Phone Registration Status" on FusionPBX
there are 3 more section on the TLS Support Aastra page
Local Certificate Filename
Private Key Filename
Trusted Certificates Filename
but I have left those blank for now
it seems getting TLS working on Aastra 67xx phones is not easy DigitalDaz
has anyone ever done it ??