Nokia is using KHTML, the engine powering KDE's Konqueror, on their phones. Apple's Webkit is KHTML with a few customizations added on.
The Nokia Web Browser is built upon S60WebKit, a port of the open source WebKit project to the S60 platform. WebKit contains the WebCore and JavaScriptCore components that Apple uses in its Safari browser. Based on KHTML and KJS from KDE's Konqueror open source project, this software has enabled Nokia to achieve improvements in Web site usability on smartphones through the re-use of a proven desktop rendering engine that has been developed and optimized by a large open source community over many years.
By the way, because the AppleTV and iPhone do not support Flash, YouTube is in the middle of reencoding all their videos in a new format they can use. (H.264) Would be nice to be able to take advantage of that.