This paper presents a method for reducing a bumblebee noise generated by a GSM technology in a smartphone. Global smartphone penetration has been very swift and 2nd generation, 3rd generation and 4 th generation communication technology are commercially used in the world. The 2nd generation wireless telephone technology is based on two standards, depending on the type of multiplexing used the Global System for Mobile Communication (GSM) and Code-Division Multiple Access (CDMA). In particular, the GSM technology has a market share of almost more than 79% in the world. GSM technology uses a channel access method that combines frequency division multiple access (FDMA) and time division multiple access (TDMA). There are four commercial frequency bands. GSM technology has a burst structure by a TDMA method. And hence, the GSM technology has a disadvantage; radiation noise is generated from an antenna propagation signal of the smartphone, and consequently, the voice quality of the smartphone is degraded. This noise is commonly known as bumblebee noise, buzz noise or TDMA noise. There have been several studies to reduce the noise since a release of GSM technology in a commercial market. Those studies mainly focused on designing infinite impulse response (IIR) notch filters by the signal processing technology or on data burst transmission schemes. The first method needs more million instructions per second (MIPS) for operation, and hence, current consumption increases accordingly. The latter method requires a change in the protocol standard of the GSM; hence, its feasibility is low. This paper presents hardware filters designed to reduce the bumblebee noise in smartphones, especially the bumblebee noise in the headset mode during calls. The bumblebee noise is easily generated in the headset mode of smartphones during calls because the headset is necessarily connected to the smartphone. This paper verified that, on an average the bumblebee noise was reduced up to 14dBm by experiments.