Hi, i bought a TP-link R488T off of amazon it is a router that require a modem
i use a tp-link 8616 ethernet modem with that to provide the link,
i use it to throttle certain ports and give other ports a higher priority
The router itself has 4 modem ports for 4 lines (bearing in mind they are not wan ports they are modem ports) for the modem that connects to the wan
Im almost certain that this device will work when i get fttc (in late 2013) as the openreach modem is a modem that connects to the wan and you have to either have a ethernet modem router or the bt hub
here this is what it states on the bt infinity for business page
BT Infinity for business requirement
To get BT Infinity for business you'll need:
a BT line or equivalent
a fibre compatible router with Ethernet WAN interface
So i hope this sorta answers your question
oh and yes this router does do load balancing (although i only have 1 adsl 8mb line)
Sources
BT Business Fibre
TP-Link 8616 modem - Amazon
TP-Link R488T Router - Amazon