It's standard practice for mobiles for many years now to implement GPRS to 3G reselection during data transfers. It might sound like a small and unimportant feature but in mobility scenarios it's very important when a subscriber losses 3G coverage during a data transfer and drops down to 2G. Without this feature the device would be stuck on the very slow 2G layer until the data transfer has finished. Quite to my surprise the same feature for LTE has only become available in mobile devices in the last year or so. My Galaxy S4 can still get stuck on 2G during data transfers or when I use it for tethering on the train and kind of 'rescues itself' to 3G rather than going back to LTE when both networks become available again. But on newer devices I have noticed that they now have the ability to also search for LTE during 2G transmission gaps and go back to LTE. That makes a real differences especially in areas where only 2G and LTE is available. In Germany that is the case in a lot of rural areas. A small feature but a big benefit to the traveling user. What's still outstanding, however, is 3G to LTE redirection/handover.