The E66 was a newer version of the Nokia E65, a voice-centric slider phone that was one of Nokia’s most successful Eseries devices at that point.
It featured the stainless-steel casing that had come to characterise Eseries phones.
The E66 also fitted with Nokia's broader strategy of putting location technology and multiple radios in its products. It offered 3.6 Mbps HSDPA, Wi-Fi and assisted GPS as well as a 3.2-megapixel camera.
Arguably the most significant improvements came in the software updates Nokia introduced on the E66 which were the biggest changes to date on any Nokia S60 device.
The E66 allowed users to toggle between two customisable home screens with different plug-ins and shortcuts, providing two views suited, for example, to business or personal purposes.
Improvements were also made to the home screen. Users could select from a range of plug-ins, which supported features such as multiple e-mail accounts, calendar and search. An intelligent search function for contacts was also added, making it more like BlackBerry and Windows Mobile devices.