Willcom D4 Teardown: Design Influenced by Quanta (page 4)
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The Bluetooth transceiver IC and other parts were mounted on the board on the back side of the keypad circuitry. The LSI possibly related to the wireless LAN function was likely to be made by an affiliate of Quanta, which took charge of the production of the D4. As mentioned above, we found a jumper wire on this board, and it implied that the handset was designed in a short period of time.