Mobile-network companies do everything they can to pull you in the door, with smartphone offerings that often come with no upfront cost. Even the most popular models are available at big discounts, with most providers offering large subsidies in order to lock you into two-year contracts.
Once you're locked in, though, costs for monthly data, text and voice plans can run well over $100 a month.
That's fine if you actually use everything you're paying for, but many people don't. One Illinois consumer advocacy group found that state residents wasted as much as $1.4 billion by signing up for more-inclusive plans than they actually needed. Threats of overage fees lure subscribers into paying for more than they use. But look at your actual usage and then see if a cheaper plan would serve you just as well.
Speaking of phone service ...