Personally I would have the master socket in the loft, it is then very easy to run your phone extensions from there and connect to the existing ones, and then a separate extension for your modem to where you require that.
You could run both data and phone in cat5e cable, use one twisted pair for the data and another twisted pair for the phone.
There's a bit of guide here http://phil.lavin.me.uk/2012/02/bts-uk-fttc-vdsl2-ex...
The data/modem cable should always be twisted pair.
Edit:You'll need a Krone tool for inserting the wires, you can get one here ( http://www.clarity.it/xcart/product.php?productid=16...
) along with other bits you'll need. They also have some very useful guides.
Or if you want the simple life the engineer will usually install where required, I just like the greater flexibility.
Edited by R0NSKI (Mon 11-Jun-12 22:18:33)