A main feature that is missing in LTE so far is a viable standardized system for voice calls for the short and medium term. Sure, 3GPP has specified CS fallback and many network operators are hoping for IMS in the long-term. However, in my opinion, both leave LTE very exposed on the voice front at least over the next couple of years.
That's why I am a fan of VOLGA, short for Voice over LTE via GAN as it offers a smooth way of connecting the already existing voice infrastructure to LTE. I've already voiced my thoughts on it here and here, but blog posts can't really go into the technical details. So with the kind support of Kineto Wireless, I've assembled a whitepaper about VOLGA to describe how it works and its advantages and disadvantages compared to other voice over IP systems for wireless networks. So if you have a bit of time and are interested in the details, have a look and enjoy!