Frank wants to get his beautiful wife, Betty, something nice for their wedding anniversary. So he decides to buy her a mobile telephone.

Betty is excited, she loves her phone. Frank shows her and explains to her all the different and varied features on the phone.

On Monday, Betty goes shopping in the local supermarket. Her phone rings and it's her husband, 'Hi ya, Betty,' he says, 'how do you like your new phone?'

Betty replies, 'I just love it, it's so small and light and your voice is clear as a bell, but there's one feature that I really don't understand though.'

'What's that, Betty?' asks the husband.

'How did you know that I was at Walmart?