This paper investigates the highly efficient design of switching mode class E power amplifier for frequencies of 900 MHz and 1800 MHz to increase the efficiency of cellular phones batteries thus by reducing the power consumed in the power amplifier. This is the continuation of an ongoing work by the authors. Here, a typical class E circuit design steps are shown for 1800 MHz in addition to the circuit designed for 900MHz. Both circuits are designed using MOSFET. The simulated results were compared with each other in terms of output power, dissipated power in the transistor, harmonics and efficiency. For this, some additional parameters are simulated and presented for better comparison. Efficiencies higher than 67% could be achieved.