I think its really naff to be honest!
I go to a pop quizz sometimes and it really pee's me off when I see peeps obviously texting their mates for the answers.
Theres one group in my local who do it all the time and when the papers get swapped around for marking, peeps have started to write 'cheats' or even just mark them wrong anyway, so it gets them nowhere.
Takes all the fun out if you have to cheat!