I've been having this issue as well. I'm on an iPhone 6s. I take great care of my phone and it's in great condition. It has NOTHING to do with people not being able to hear me though. I cannot hear any audio in the ear piece nor is anything going out via the mic. This happened immediately after my iOS 11 update. It's not my phone. The phone was completely fine. I restart, it works just like many others have stated. This is a big problem as I handle multiple client calls daily. It's messing things up for me. Causing major frustrations. Also, the freezing and random restarting is absolutely getting on my nerves. I've never had a problem with iOS updated as I have with this.
Anyone experiencing weird cellular service slowdowns drop outs? I had great service and now, it's really bad. My web browsing is faster via my wifi as opposed to my data connection. Which is just odd and again, only after I updated. I updated to 11.0.1... things are buggier now with apps than initially. This is not good.