FCC Mandates that AT&T and Verizon Allow Data Roaming

What the big issue at hand is the sunset of dedicated voice systems. Within a few years, there will not be "voice traffic" and "data traffic", but all voice traffic will be carried via data, therefore no data roaming will equal no voice roaming. The carriers aren't going to develop a dedicated LTE voice system and a dedicated LTE data system, it's all going to be going through a single LTE data system, including emergency calls such as 911.

Once the carriers start rolling out LTE, it won't take long and they're going to have incentives for consumers to switch so the current GSM and CDMA systems can be decommissioned, just like the analog and TDMA systems of yesteryear. They don't want to maintain many different networks, and the only company that is currently content doing that is Sprint. (Sprint is unifying systems, but could have chose to start that process much sooner.)

The other issue at hand is that the large carriers have control over so much spectrum that start-up companies have a huge barrier of entry. There are many places, including the rural areas, where AT&T and Verizon have huge swaths of spectrum licensed (not owned) but use only a tiny portion of that, preventing other companies from acquiring it to actually use for customers.