A Federal Trade Commission investigation, which found certain pre-paid calling cards offered an average of just 40 percent of call minutes.

Is your phone card phony? 5 ways you can tell

When is an hour just 36 minutes? When you buy some phone cards, apparently. That’s the conclusion of a recent Federal Trade Commission investigation, which found certain pre-paid calling cards offered an average of just 40 percent of call minutes customers thought they were buying — and some, significantly less.