I am having the same problem it seems as others on this thread, trying to find the contact button on your profile but can't seem to find it. Have a Avaya hard phone, works on Home Hub 3b, but not on the HH5. Sounds like the same issue with getting the SIP ALG disabled. The phone logs into the system from home to work via VPN however does not have any dial tone and is missing other functionality to make calls.
Is this something that you could help arrange?
We can certainly look into it to see if the old fix is applicable on your Hub 5's current software. You can reach us by clicking on my user name and then on contact the mods. Please note; there is a delay responding to tickets (at least 5 working days). We'll get back in touch with you as soon as we can though.