https://documentation.avaya.com/bun...erR11.0/page/Remote_HTTP_Extensions.html

At the office, you need a Static Public IP Address, the Internet modem should be set in Bridge mode, and they need a real firewall.
In the firewall, you allow connections on ports 1719, 1720, and 46750 through 50750 (but verify the RTP range on the VoIP tab of the IPO's LAN port)
The firewall must BLOCK connections on those ports from any other source, or you WILL be hacked

At this point, you might as well program an IPSec VPN on the firewall, program the built in IPSec VPN in the 9608 phone, and now the phone can connect from anywhere, even if the home's public ip changes, or you eventually need more remote phones.