A cellular phone having a first opening for delivering voice on a shell is provided. A printed circuit board (PCB) is disposed within an inner space enclosed by the shell and divides the inner space into a first acoustic room and a second acoustic room. A speaker is disposed within the first acoustic room and electrically connects the PCB. A through hole is formed on the PCB to communicate the first acoustic room and the second acoustic room to increase the size of total resonance chamber for improving resonance effect in low frequency voices. Furthermore, at least a second opening is formed on the shell to communicate the first acoustic room or the second acoustic room to the environment for flattening the resonance curve to improve the voice quality.