Tesco Mobile
http://www.tm-standardplus.co.uk/
Virgin Mobile
http://www.virginmobile.com/promo/duoSim.html
T Mobile
http://www.t-mobilesimgiveaway.co.uk/
Orange
http://shop.orange.co.uk/shop/homepagefreesim
O2
http://freesim.o2.co.uk/messages.php
BLYK (Never used them apparently only for 16-24 year olds)
http://www.blyk.co.uk/lp_free
http://www.tm-standardplus.co.uk/
Virgin Mobile
http://www.virginmobile.com/promo/duoSim.html
T Mobile
http://www.t-mobilesimgiveaway.co.uk/
Orange
http://shop.orange.co.uk/shop/homepagefreesim
O2
http://freesim.o2.co.uk/messages.php
BLYK (Never used them apparently only for 16-24 year olds)
http://www.blyk.co.uk/lp_free