I don't really like feeling stupid. I don't mind feeling comparatively stupid, if it's relative to smart people. But it seems I'm stumped by something that even the dimmest teenager can do. Something that millions of them manage. Probably pre-teens as well. I can't activate a mobile phone sim.

I've got a spare (Vodafone) phone. I've got a pack with a Vodafone PAYG sim in it. All I need to do is get to the stage where I can top up the sim and make/receive calls. The paperwork with the sim says call 17298 on the phone and you're away. I call that number and it says do the whole thing online instead. So I've tried. I've setup my account at Vodafone.co.uk. But there is no option to activate a new PAYG sim. I've searched. And no one on the internet seems to have had this problem. So I've tried registering that phone for 'Pay as you go talk services'. Maybe that's just a fancy way of saying they'll make the phone work. So I click on it, it asks for the phone number, it says it will send a security number to the phone as a text... but the text never arrives. I've even tried going out and buying another sim pack in case the first one was faulty. Dim thirteen-year-olds who get chewing-gum in their hair can do this while playing on their Nintendo DSs. Why can't I?