Pay-per-use cellphone plans are sometimes befuddling -- the rates can change depending on whether you're calling or texting, or how much cash you put on your account. T-Mobile thinks it can end this confusion with its new, much simpler Pay as You Go plan. As long as you plunk down at least $3 per month, it costs 10 cents for every text message or minute's worth of talk time; you won't have to guess how much credit you have left after a long call. It should be cheaper in some cases, too. Previously, you had to pay as much as 33 cents per minute for voice if you only bought small Pay as You Go refills.