System, apparatus and method of optical communication are provided for performing efficient channel estimation for a CO-OFDM link utilizing an intra-symbol frequency-domain averaging to compensate for transmission impairments. In particular embodiments, the system is optimized for identifying the smallest available locker that would accommodate the parcel, and facilitating delivery of the parcel to that locker. It receives instructions of a first type from the central processing unit and instructions of at least a second kind which are stored in the memory external to the central processing unit. Therefore, it is possible to use only a main module and sub-module that have been inspected after manufacture and found to be non-defective. The mobile receiver receives GPS signals, performs rudimentary signal processing and transmits the processed signals to the wireless carrier. In an embodiment, the method comprises initiating a standby mode upon actuation of a standby key in the handheld electronic device; displaying a confirmation message of entry into the standby mode; and disabling at least one feature of the handheld electronic device upon entry into the standby mode.