The current version of software for the HTC One M8 on the Sprint web site is 3.30.651.2. The small update is version 3.31.651.2 that was received on 12/19.
I have bought a couple of phones off craigslist and have not had problems with either. The first was a Nexus 4 that I took overseas and the other was an HTC One M7. When I returned, I sold the Nexus 4 for what I paid for it. I still have the M7.
I'm sure there are lots more people on this board the have knowledge about texting, but I believe that there is no guarantee that a text message will actually be received and there text messages are not a priority for the network. My HTC One M8 has and app called emergency alerts. I would look at something like that for your 911 center.
Seventeen fake cellphone towers were discovered across the U.S. last week, according to a report in Popular Science.
http://www.businessinsider.com/mysterious-fake-cellphone-towers-intercept-calls-2014-9
I have a friend who use to work at US Cellular in Chicago. His comments are how they are hurting financially and need help. Sprint has already bought some of US Cellular spectrum, so it doesn't seem a big leap to buyout the remainder of the company.
I did not notice until today, the HD icon when I dialed from the dialer. It is green, I circled it. I'm not talking about the HD phone Icon on the top. The connection was between and HTC One M8 and an Iphone 5s.