I can believe anything, provided that it is quite incredible - Oscar Wilde
Apparently the new messaging and media player gizmo will be based upon an unspecified Linux based operating system. The Mylo is based on the Trolltech Qtopia Platform, which is a new graphics and application development system that features a plug-in framework aimed at multi-function consumer electronics devices. The layered, multi-coloured approach of the Qtopia framework is pictured below.

Qtopia has enabled the device's developers to have quickly incorparated, among other features, the Google talk, Skype funtionality and the plethora of media playback options, into the device.
Trolltech, when launching the Qtopia Platform, initially said the system would support the Linux Edition of the Wind River produced 'Platform for Consumer Electronics'. Therefore its likely the Sony Mylo may well be the first high-profile consumer electronics device to incorporate the embedded Linux OS from Wind River.
This stack enables Java Virtual Machine support, which would seem to give homebrewers plenty of options for developing home made apps for the device. It will be interesting to see how far Sony attempts to lock the device down - noone wants a similar situation to the regular patching the PSP 'requires'. µ