Each mobile phone functions at a certain frequency of wireless data transmission. 900 MHz and 1800MHz are the frequencies used for voice connections and GSM signal transmission (SMS / Voice calls / GPRS / EDGE). The majority of mobile providers in Kenya and most countries all worldwide use 900MHz as a standard frequency, while 1800MHz is an additional frequency band. If you need to amplify not only GSM voice connections but also 3G network you can choose dualband or triband signal booster. These indoor GSM repeater models amplify two or three different frequencies or signal types at a time, e.g calls at 900/1800 MHz and 3G internet at 2100 MHz.