internet -> PLDT modem (i1) -> TL-R470T+
internet -> PLDT modem (i2) -> TL-R470T+
internet -> PLDT modem (i3) -> TL-R470T+
As what @
Jhunax said, It usually need to be setup and we REALLY don't know how intelligent that load balancing device of yours is, Does it "auto configures" anything whatever is plug into it?.
As far as I have known with load balancing units, the IP's, Subnets, gateways, etc... 'coming into' the TL-R470T+ MUST be UNIQUE!!!... If modem i1 gateway is 192.168.1.1 and modem i2 gateway is also the same as i1, then you have a headache
however..., if you configure the modems (i1, i2, ix) to bridge mode/PPPoE (if modem supports it) , then, you may have a good chance!
Good Luck!