Sony Ericsson has announced that they are acquiring UIQ from Symbian. UIQ Technology (and the UIQ platform) has been tapped by Sony Ericsson for years in their popular P-series devices. Like Series 60 on Nokia, UIQ has been predominantly used by Sony Ericsson, on their popular P-class series of smart devices.
Both Series 60 (S60) and UIQ are powered by the same core, Symbian OS. UIQ differs from S60 in that it is aimed at devices with touch-screens, and generally have higher processing power. Under the purchase agreement, Sony Ericsson (which is a minority shareholder in Symbian itself) will continue to have access to the Symbian OS, while having complete control of the UIQ platform.
Sony Ericsson and UIQ Technology have been working closely for years, UIQ Version 3.0 (which is tapped in the P990, M600, and W850) was heavily influenced by Sony Ericsson developers.