You are correct, you need a A/B line spliter that seperates the "pairs" (line 1 and line 2) of your phone phone wiring. FYI, standard telephone "voice" jacks are RJ11. New modern wiring are going to RJ45 which was used for network "data" jacks. Note RJ45 jacks are backwards compatable with RJ11.
As far as household telephone wiring, at the minimum there should be 4 wires, 2 pairs, each pair equals one line. Ooma only supports one line. One can make use of a 2 line system with the Scout providing the second pair of wire, in the case of the Telo one would have to buy a second Telo to provide a physical 2nd line connection like the Scout does.