The Nokia N91 is a mobile phone that was released to the public in April of 2006. It is part of the Nokia Nseries range of mobile phones. It features a 2-megapixel camera and a 4GB (8GB in the "new" 2006 version) hard disk to store approximately 3,000 songs encoded in either AAC, AAC+, eAAC+, MP3, mp3PRO, WAV, MIDI, or Microsoft's WMA format. It also features 3G and wi-fi technology. The phone features a 176 x 208, 262,144 colours TFT LCD display and dedicated music functionality buttons (XpressMusic) that slide down to reveal traditional mobile phone keys. Battery life when solely playing music has been estimated at 12 hours.