I had the very same issue a year or two ago with my HTC EVO LTE, after complaining to Sprint they reprovisioned it and suddenly it worked fine until last month upgraded to the m8.
Is there any better rom or firmware that can help me with this? As long as it has a good strong signal, it's fine but unfortunately we're I live and travel to, Sprint's coverage is poor but still it's frustrating that it doesn't even seem to work roaming when it picks up other service towers as it warns me I'm roaming and addtional charges may be encurred. I have called Sprint and they deny there is any issue with their service yet all the Sprint stores in my area and the Sprint vendors strongly urged me to upgrade to the iPhone instead of an android phone as they all repeated the same story that in my area, Android phones don't work well and from what I have seen the are right.
Any words of advice or suggestions? I'm still in my grace period were I can return the phone, Sprint technical support is suggesting I return the phone as it might be defective which I might believe expect this one is doing the same as my prior until Sprint did something "special" to the old one which fixed it but now they claim it's not their problem.
In a nutshell, it comes to be a issue with the Android phone type as when this M8 won't work, other Sprint phones do such as iPhone and an older Kyocera flip phone which the Kyocera phone was the one I had to use to call Sprint as my M8 couldn't maintain a voice call connection longer than 10 to 20 seconds before it would drop the call.
I'm totally frustrated, any suggestions?