CELCOM 3G INSIDE BUILDINGS

I have mixed experiences for Celcom 3G signals inside buildings. As a radiologists, we usually worked inside rooms, mainly barium plastered rooms to shield the radiation from radiation emitting sources such as CT or Angiograms. Have mixed experiences on Celcom signals. In Kuantan Hospital, when i am inside the room, i only get GPRS signal. No 3G. Whereas, for Digi, I managed to get EDGE signal. However in Cheras, within the hospital building, Digi signal is very poor, to get a GPRS signal is very good already. However for Celcom, I can get full bar HSDPA signal. In Batu Pahat, Johor, I only get a GPRS signal inside the room. However for Digi, i can get an EDGE signal, even though it is only 2 bars. At home in Kuantan, as i mentioned in the previous post, I can get 3G signal for Celcom. Maybe this is due to the positioning of the Celcom and Digi towers. Or is it due to the wavelength of the Telco signals? Only a technical person can tell me about this.