Unfortunately it's very difficult to make a nice job of connecting to the system. I usually just use x connect wire hooked up to the existing wiring panel. Up here in Canada we use Bix connectors for all new work, all the old wiring was terminated on 66 blocks.
It never ends up looking like a nicely terminated amp end but you get what you get.
Also, I'm not sure if everyone knows about it but you only have to terminate the outside pair for digital phones. The inside pair is for analog phones. I do this so there's less wires inside the cabinet, and also if the customer wants to swap an analog for a digital phone or vice versa, I have to come do a service call
