The BenQ-Siemens SL91 is a slider-type GSM 3G mobile phone. Its name came about because of BenQ's acquisition of Siemens' mobile communication division at the end of 2005; the Benq-Siemens brand is meant to be transitory, before all phones are produced under the BenQ brand.

The phone supports GPRS and UMTS Internet access methods. Its dimensions are 89 mm × 47 mm × 23 mm, and it weighs 109 grams. The supplied battery has a capacity of 950 mAh and can last up to 310 hours in standby mode, or 195 minutes if the phone is used for calls. Other notable features of the phone include Touch-sensitive navigation keys using FSR (Force-Sensing Resistor) Technology, MP3/AAC player, Bluetooth, a Java virtual machine, FM radio, 16M colors QVGA TFT LCD, and 3.2 megapixel camera with autofocus.