Hello,
Looks router cannot be used via any of it's wan interfaces - ethernet or sfp/sfp+ one. The sfp stick that comes with looks to be pretty standard on 1270/1310 nm, and the gpon OLT makes the pon connection and sees the mac address of the stick. Good up to here, however as the router does not communicate over the pon link. I assume the router is set with a vlan, so ethernet frames are not understood by the gpon. Will try to find this out, but if there is a vlan tag as I assume, I cannot use the device as a router.
The good news is that if I connect the router via a pon media converter (those are for $8 from China and work just perfect) to one of the lan ports, disable the dhcp on the BGW router (thanks AT&T, this is possible!), and enable the dhcp on the pon box, the router becomes a 4 port switch with an excellent wifi attached. So, the pon box distributes the dhcp configuration, and the BGW320 becomes a switch with wifi. Pretty useful, looks to work well.
Just to note that my telephone was able to show 2401 Mb/s over-the -air wifi connection - pretty decent.