7. "I'll get the cheaper mobile phone plan and just keep a really close eye on my texting and talking."
Unless you've gotten a landline and ditched your cell phone because you don't have a job with a boss and coworkers who text you and don't have a teenager who texts, you are likely to text just as much this month as you did last. So if, on average, you use about 500 texts a month, pushing your plan down to 200 will not work; you will go over. And rather than saving that extra $10, you will now be charged 10 cents per text. The math doesn't lie: You have now spent $20 more.