A mobile handheld electronic device having a given form factor includes a detachable cellular telephone carried within the mobile handheld electronic device, such that when the cellular telephone is positioned within the mobile handheld electronic device the form factor is unaltered. The mobile electronic device includes structure for establishing and maintaining a mechanical connection between the cellular telephone and the mobile handheld electronic device when the cellular telephone is carried within the mobile handheld electronic device, and structure for establishing an electrical connection between the cellular telephone and the mobile handheld electronic device when the cellular telephone is carried within the mobile handheld electronic device. Preferably, the cellular telephone has a battery distinct from a battery in the mobile handheld electronic device, and the cellular telephone battery is recharged when the cellular telephone is carried within the mobile handheld electronic device. When the cellular telephone is docked within the larger device, given data on the cellular telephone is synchronized with given data stored in the mobile handheld electronic device.