Is it possible that "com.android.server.telecom" will be shown in the activity history even if we don't call any one or receive any one, not even internet calls ?
Welcome to Android Central! Yes, I believe it's possible. Apps can still be active -- it could be something simple like pinging the server. I wouldn't worry about it.
The phone has to keep the towers notified of which tower it's connected to - or if you're out driving, you may get a call on a tower miles from you and never know it. That's been part of the "cellular" concept from the beginning, back in 1979. (Some phones don't log pinging, because people ask about seeing it in the log ... as you did.)