too bad, i am not able to telnet into the hg850a

btw, just found that maxis VOIP doesn't seems require vlan other than vlan621.
my setup as below work, just it is with additional thompson router in place:

[huawei btu] LAN 2 --> [my own router configured with vlan 621 tagging] <-- [thompson router] wan to any port of my own router

Thompson eVOIP connected with IPOE succesfully.