I am using 4 Voltek, CT 122 Cameras on my house. But the one on the front cannot read number plates. So I have been told, the Voltek vpcdn2 is much sharper? (more pixels)? Or can you recomend a camera for me? (colour). That I can connect to, 6-pin-mini socket, and 6-way/RJ11 plug?

There are 2 issues here. Systems such as this are not normally used for recognition capture. If you want to capture regs then lens size or scene width are the most important aspect. You want to be viewing approx a scene width of approx 6m at the point of reg capture. You also need to be facing the reg in question with the camera. Too much offset angle will make it harder.