蜂窝 = honeycomb. Cellular networks divide coverage into hexagonal 'cells' that look like a honeycomb on planning maps — same metaphor as the English 'cellular.'
usage
On iPhones in Chinese, the toggle is labeled 蜂窝网络 / 蜂窝数据. On Android, you'll more often see 移动网络 (yídòng wǎngluò) or 移动数据 (yídòng shùjù).
