I have a USB drive plugged into the HG659 and I have enabled sharing via FTP and Samba, created user accounts for FTP and enabled anonymous FTP access. I have also added ACL to enable FTP both on the LAN and WAN but I have left the "Starting IP" and "Ending IP" fields blank as I don't the IP addresses from which I am going to be doing the FTP.
Access from LAN works fine but not over the WAN using the modem external IP address from an external site (error 503: the user is forbidden).
Has anyone done this successfully? If so, can you share how you got things to work for WAN access?
I'm facing the same problem. I have contacted Huawei, as you suggested and Huawei has advised I need the password for the "root" user to be able to change the ACL configuration for FTP from LAN to WAN under the Network Security of the modem.
They have advised that as the modem has been sold by TPG you are responsible to provide the password for the "root" user.