A reconfigurable multiple-input multiple-output (MIMO) antenna design for the smartphone with a metal frame capable of covering hepta-band LTE/WWAN is proposed. The proposed antenna has four monopole slots (two long slots and two short slots) etched on the top and bottom side of the system ground, respectively. Two PIN diodes are inserted into the two long monopole slots. When these two PIN diodes are OFF, the two long monopole slots can generate the desired lower-band (824–960 MHz) which can be applied in a 2 × 2 MIMO system. When these two PIN diodes are ON, the corresponding lengths of these two long slots are decreased to the same length as the short slots. Then these four ports can excite the desired upper-band (1710–2690 MHz) which can be used for a 4 × 4 MIMO system. In addition, the performances of the proposed antenna including the return loss, isolation, efficiency, envelop correlation coefficient, mean effective gain, and channel capacity are presented.