Can Applications developed using Qt framework be deployed in all the Nokia devices. And Series 40, Series 60, Meamo cover all the Nokia devices available? How can we identify that an Qt app can be deployed in a Nokia device?
I would say, the application should run on any device, where you are able to install the required Qt and QtMobility backend (until today the backend is not built into the operating system... although I would guess that this will be the case with the new MeeGo devices - but that's really just a guess).
In theory, Qt runs on S60 platforms from 3rd Edition FP1 (3.1) onwards. See the device matrix on Forum Nokia to see which devices have S60 3.1 or newer. In practice, some devices may have compatibility or resource (in particular, memory) issues. To be sure, you'll have to test on all devices you want to officially support.
Also, Qt is available on Maemo 5 devices (N900). Qt 4.6.2 is preinstalled on N900 PR 1.2 software update.
Series 40 is not supported.
In any case, the same application cannot be deployed on both S60 and Maemo. You'll have to build and package it for each platform.