starting up - How to set up an 0844 number ?

I'm going to start a cheap long distance calling service and would like to have 0844 numbers from 0.5p to 5p as other players have.

My question are:

a. How do I apply for such numbers ?
b. What's the expected net profit on the actual amount the user pays per minute.
c. Are there any providers who lease these ? should I then forward them to my channel supplier (i.e VoxBone ?)

Thx

Ben