The small yellow thing is a "Block terminal" essentialy not a master socket, it's just a connection point between your drop wire and the internal Cable (lead-in) which leads up to what you describe as the master socket. and this is all part of BTw monopoly wiring. To get this moved/changed etc is done by BT and yes will involve a charge.
From the
master socket faceplate you can fit your own internal wiring, the best cheepest way is obtaining cableing from a diy store along with an insertion tool, the basic ones cost about 70p but if your going to fit a number of sockets it's worth investing in the full blown idc tool as it makes life a lot easyer.
Colour codes, blue wire with white rings go in termination number 2,
white wire with blue rings go in termination number 5 (both of these are the voice & dsl wires)
Orange wire with white rings goes in no.3 (bell wire which gets phones to ring in all your extentions)
any others are spare, so if you have a 2nd line a single 6 wire cable can support this.
Spere wires don't coild them around the cable, looks neat, old practice but causes problems with data, and the same thing don't coild them round in a nice ring, (coil the surplus in a coil then flatten the coil so they just run back & forth
Don't put more than 3 wires in any idc, always hold the insertion tool straight before terminating (failure on both these can cause a fault which is infuriating to locate)
Run cable at least 50mm away from mains cables for any lenght.
run the cable along the top of skirting boards and around the top of door frames.
Never under carpet or across high foot traffic areas such as the floors across doors (guaranteed fault sometime in the future)
If you have a profiled skiting board then running the cable along the profile is ideal as particuarly after a coat of paint it should really look as it its part of the moulding. (only problem here is if some one later cuts through the cable while working on the skirting board. spent hour one morling with an 85m run only for the dial tone to dissapear mid test. Then found the chippys mate complete with saw in hand
)
Only use staples if the stapler is tapered (otherwise your guaranteed to pass a staple somewhere through the cable) don't use a stapler if the staples are tight on the cable causing a pin-cusion effect (lots of little dsl faults)
Easyest method is to use cleats, not as pretty, but a lot easyer.
And before putting a staple/cleat in make sure your not about to put it through an exising cable which looks like part of a door frame/skirting board (done that my 1st time
)
If your looking to completely sort everything, best option is look to use an adsl face plate. The main problem is the master socket is the only plase with a dsl signal, all your extentions will just have normal telephony. You can have brand new perfectly fitted extention wiring & still find it kills your internet connection
Or stuff the whole idea and just go for cordless, phones and router
(I've also listed all this in case anyone reading this is thinking/doing the same or trying to locate what might be causing an issue on dsl with their internal wiring)