Allows your drunk taxi friend to take payment for services via your credit card. Before he drops you off, he'll know whether your credit card is good or not.
Frank picked Jon up from Bumpys and took him home. Jon flashed his credit card, but Frank had no idea whether the card was good. Therefore, he go mobile commerce'd it up and took payment before Jon went inside. The card was good and Frank was happy. Both Frank and Jon slept well at night.