Here’s one way …

A cousin of mine didn’t get (or maybe “didn’t want”) a cellphone while he was so young. So he never bothered to push his parents for one over the years.

Then, over this summer, he started borrowing his mom’s cellphone to send text messages. When the bill came, it was high enough that his parents decided he needed a cellphone of his own with a mobile-plan to match his needs.
How many theories does this prove:
1) That is how you make a business case.
2) The power of the network effect. Even when you don’t care about something, enough of your peers have/use it that you need to start using it too.
3) It is always easier to prove the ROI with hard facts/numbers (in this case, the bill)
In his own, SMS version of the story …

strtd textin wid mums cell…and d bill amt roktd to d dey brought me a cell