@ kowenicki
£30 times 18 is 540 pounds, a PS3 costs the company ~240 pound or less (Sony is taking losses), a Samsung phone ~100 pounds or less (the phones are expensive for consumers to buy standalone intentionally, but not that expensive really for retailers). So for the rest you pay at least ~200 pounds per 18 months, about 11.10 pounds per month (including taxes).
For 10 pounds if you have a phone already you probably have a similar contract from the same or other provider. For example in the Netherlands standalone contracts for 2 and a half Euros (~2 pounds), 120 minutes per month and 20 SMS, outside the contract it becomes expensive, the companies take this into account as well, they don't generate huge profits for nothing.