The tight integration increases performance of Qt applications. Qt in Symbian is highly integrated to the operating system features, such as graphics and file system. The relevant modules are automatically added via Smart Installer, which checks for dependencies during installation of Qt-based applications.
Symbian phones starting from S60 3rd Edition, Feature Pack 1 have had Qt support through downloadable modules. The latest Symbian Belle phones include Qt as part of their firmware, and earlier phones have Qt support pre-installed as well. Qt is an integral part of the Symbian platform. 1.4 Key Features of Symbian Development.
