SBG3500's multiple Vlan

It seems the ISP have VLAN 6 as untagged then 4 & 8 as tagged. Can he then not 'simply' create VLAN 4 & 8 and set let's say port lan 2 to VLAN 4 untagged & port lan 3 to VLAN 8 untagged?

Then the unit(s) that connect to let's say port lan 2 (on VLAN 4) gets IP from the ISPs DHCP server on this VLAN. Which I believe would be the practice for most ISPs when providing IPTV, all IPTV boxes/units get their own IP directly from ISP rather than local IP from the gateway/router.

Johan all services are in Vlans over PPPOE, and the internet service is on the ISP default routers set as untagged (trunked).

      ------PPPOE------\
      === Vlan4 voip ==> \     --------------------------------  ==> VLAN4=> Voip        VLAN4 tagged
ISP=== Vlan6 Inet  ==>      |Router DHCP_client @ Vlan6|  ==> VLAN6-> default/VLAN6 untagged
      === Vlan8 iptv  ==> /    --------------------------------   ==> VLAN8=> iptv        VLAN8 tagged
      --------------------/