Thanks for your reply. So if I put on £10 right now, it will start working straight away? or will I have to wait?
I forgot to add this above. I got a text saying "02: great, you now have 1000 mins/texts for your 02 numbers this month. your next £5 payment will be taken on 8th feb 10. for help text remind me to 21300'
So this is why I thought it would work even though I don't have enough credit?