Master splitter installation

I purchased a master splitter to install , and have found the existing phone line in the ceiling.

I can join the line to this, and then run a cat 5 cable and use two pairs for the two rj 45 sockets.

Is someone able to help with what the pins are on the rj45 ? 4,5 for voice and 4,5 for data on the other ?

Also the rj45 to rj12 lead to the modem line input. Is this the two centre ones also ?

Thanks in advance

Tom