Teenager phenom takes Nashville by storm? Wait, this story sounds so familiar. But this time, it’s not about Taylor Swift. It’s the boy version, times two. The Carter Twins are Music City’s newest duo, full of innocent songwriting and sweet harmonies and electric guitars and playful keyboards. They even blog incessantly about their personal lives. Josh and Zach Carter are just 18, but already they’ve got producer Frank Rogers and other industry big shots behind them. The debut single, “Heart Like Memphis,” is about that kind of good girl who gives the world her best and calls her mom every day. But underneath all that perfection is a heart like Memphis. So if you’d been waiting for a country version of the Jonas Brothers, maybe the Carter Twins are your guys. All that’s missing are the posters for every tween girl in America.