Yes, that is the problem with Celcom at my house area. When I was using Celcom, my phone wouldn't ring then few minutes later I'd get an SMS about how I have a couple of missed calls. When I called Celcom with regards to this issue, they told me they don't know what's wrong coz they checked my house address and it's within coverage area. They asked me to give them some time to investigate. Sure enough, a couple of days later I received a call from their officer who told me that my house (and a few other houses nearby) was in this grey area which is in between two towers and therefore the coverage was inconsistent. There is no solution to his unless they put up another tower which they won't.