In mobile phones and several other wireless communication devices, antenna is an important element which decides the quality & performance of the device over various communication standards. In this paper, a compact internal Planar Inverted-F Antenna (PIFA) with a ground plane having two open ended slots is proposed which is very thin compared to conventional PIFA structure. By using the ground plane as a radiator element along with top plate of PIFA structure, the height of PIFA can be reduced to a great extent, which further results in reducing thickness of mobile phones. In this paper the proposed antenna has volume as 25 x 15 x 3.8 mm3 and it is simulated & analyzed using HFSS software. The antenna is designed to operate at GPS, GLONASS, DCS (1800 MHz), PCS (1900 MHz), UMTS (2100 MHz), Bluetooth (2400 MHz), 4G LTE (2300 MHz & 2600 MHz), WLAN (5.2 GHz) standards. The simulation results show that the performance parameters of the antenna are satisfying the requirements of advance wireless communication devices.