A small ultra-thin planar inverted-F antenna (PIFA) which can be switchable or tunable using PIN or varactor diodes, respectively, is proposed. The antenna consists of two radiators and connected together using two PIN or varactors diodes. Frequency reconfigurability is obtained by (i) tuning using varactor diodes or (ii) switching using PIN diodes. In the study, when varactors are used, the PIFA is optimized to operate in five frequency bands centered at 0.72, 1.35, 1.98, 3.6, and 5 GHz. Varying the voltages across the varactors can tune these five bands over the range of 45.33% (0.58–0.92 GHz), 17.77% (1.23–1.47 GHz), 26% (1.57–2.04 GHz), 6.66% (3.48–3.72 GHz), and 0.97% (4.99–5.04 MHz), covering the DVB-H, GSM 800/900, GPS, PCS, DCS, UMTS, Wibro phase III, WiMAX, WLAN systems, etc. If PIN diode switches are used instead, the frequency bands can be switched among different standards, including the DVB-H, GSM, UMTS, DCS, GPS, WiMAX, and WLAN systems, depending on the switching states. The two radiators are supported using a shorting wall and a shorting pin connected to a small ground plane. Results of intensive investigations using computer simulations and measurements show that the ground plane size has little effects on the performance of the antenna. The effects of user's hand on the S11, radiation patterns and efficiency are also characterized.