I've had this same issue and got a new SIM card and did a hard reset of the device. No problems since. There is a maintenance update HTC is working on but no timeline as to when it will be released
I cleaned mine about 3weeks ago been fine so far
I started getting the "Preparing SIM Card" today after installing a battery saving program that disables the data connections after a set period of time. I would get the message along with the np service indicator after waking the phone and when it attempts to establish the data connection. It would usually pop up 2x then I would have service and data again. I uninstalled the program as I never had this before installing it. Hopefully this fixes that issue.
When I installed Opera mobile on my DNA, got the No SIM message twice. Uninstalled it and haven't since. I wonder if there is a weird software problem causing this.
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