My Droid Maxx has been doing this for the last week or two. It seems to only happen at night though. I have a full 4g LTE signal, however it changes from grey to blue constantly. I am able to text, search the web, or plain just do anything else...other than call out or receive a phone call.
When I try and call it just says dialing or retrying.
Has anyone else had this same issue? I have searched my phone for any time settings that may be keeping me from making or receiving calls during certain hours since this only happens at night when I am at work but have not found anything.