Thought this might be useful:
http://www.o2deals.co.uk/o2 deals is now offering Pay as You Go o2 sim cards which offer 500 free text messages a month (to any network) for FREE
Or, if you're more of a talker than a texter, you may prefer to select one of the other free allowances available with your Online Pay & Go SIM. Choose either 100 FREE anytime any UK network minutes or 150 off-peak any UK network minutes every month - the choice is yours. Details of how to select the option you prefer will be sent to you with your SIMs. These sim cards were formerly known as genie sim cards.