Sprint wants everyone to know about its tri-band LTE network that could potentially reach speeds of 50 - 60 Mbps, so it gave it a catchy name - Sprint Spark. Once the rollout is complete, this could be the largest LTE network in the US in terms of spectrum usage. But that's the future. Right now, the network is available in only a handful of cities (Chicago, Los Angeles, Miami, New York, and Tampa), and even fewer phones are currently set to tap into it (okay, just one). Fortunately, a couple of handsets will soon receive the OTA they need to make the leap.
The MK1 and MK2 software updates provide the Galaxy Mega and the Galaxy S4 Mini with access to Sprint's faster LTE bands. Unlike the two Samsung devices, the HTC One Max already ships with support for these bands enabled out of the box, so its OTA just provides vague "LTE UI Enhancements."
Put bluntly, this update won't affect all that many people just yet. But if you live in one of the aforementioned cities and happen to own one of these specific devices, browsing using Sprint's data network should become gradually less painful soon enough.