you can get upto 4 o2 sims on the 2 o2 links and 1 sim card on the orange link

http://o2freesims.co.uk/
http://mates.o2.co.uk/Index.aspx
http://shop.orange.co.uk/shop/simoffer

ive had loads of them sent to me in the past and have asked for more

with the o2 sims you get 100 free anytime/network mins a month or 300 free txts a month when topping up with just a tenner.