I've preached this here a few times and I know a few users have benefited but if you have access to an O2 or unlocked phone, abusing Pay and Go sims still works and is amazing value. Total effort takes about 10-15 minutes per sim (but a few days waiting for delivery) and you get £20 of PSN credit for ~£10. If you go through Quidco (or TCB) you also get £5 (or £5.50) back meaning the final cost is £5 for £20 of credit. You can do this up to 3 times per month for a total of £60 PSN credit. Full instructions are here (read the top rated comments for up to date steps to follow):
http://www.hotukdeals.com/deals/possible-free-30-o2-pay-go-sim-10-top-up-required-2181487
Don't want to clog up the thread so if anyone wants to try it and needs some advice, feel free to PM me
Not if you use a mobile browser. They accept Paypal then. Ordered one myself about an hour ago