4G LTE was a huge jump forward for cellular networks. It allows voice and text messages to use cellular data to send and receive information instead of relying on a separate channel. Plus, it bumped up mobile data speeds to higher than most home broadband connections.
Unfortunately, it now looks like it also brought a serious security problem. Carnegie Mellon University's CERT came out with an advisory listing some ways that LTE isn't safe, including allowing hackers to spoof numbers for phone calls and text messages, get free video calling, and even launch denial-of-service attacks on the cellular network.
The problem has to do with the protocol used for voice calls and text messages on LTE, called Session Initiation Protocol. It has several weaknesses that let hackers in, and unfortunately there isn't any easy way to fix it.
The danger for you from this kind of attack is that hackers could eavesdrop on your conversations or make your phone call premium services and shoot your phone bill through the roof. At least, that's the case if you're using an Android smartphone on two particular networks.