At first I didn't think that was such a big problem, because it happened only every now and then, but now it's becoming frustrating, because I missed some important calls because of it. Long story short: Sometimes I simply won't receive a call, instead I get a missed call notification, sometimes even few minutes after I was called. 'Do not disturb' is turned off, so that cannot be a problem. Sometimes I don't receive a call even while using a phone. Has anyone else had such problems before?