faulty mobile phone- my rights?

Hi,
I have been with three mobile for around 5-6 years, in june 2012 i upgraded my phone as per usual, my problem is that in the last couple of months of being a bit temperamental my phone powered off and will not work at all, so after 7 months of my contract i now have no phone, its a htc one x which is pretty high end and i am a small business user so need it for work.
I intend to take it back but am wondering about my rights as to what i should be asking for, should i just ask for a brand new phone to replace it or as i am expecting should the shop offer a repair first ? i know the shop will probably not be willing to offer a new phone straight away but i can really do without this dragging on..
does anyone have any thoughts/ been in the same situation or know the actual laws relating to this so at least i have some ammunition before i go in..

many thanks in advance
simon

hi thanks for the replies,

i took the phone in this morning and got the response i was expecting, that they would send the phone away first for repair if possible, however they then told me that they only have 10 courtesy phones all of which are out already, so they could not offer me a phone. i hadn't read the second post from witchconsumer so i think my next course of action will be to return tomorrow and make sure that i have a phone to use while they repair mine..

thanks again for the replies

simon