Hi Heinz,
>> Is it possible to use different themes in one WebServer depending on the sessions?
yes, and as you pointed out, for Desktop it works well.
For Mobile it's going to work less well, because the mobile app doesn't refresh the pages in the same way.
I would say, for mobile users, it's going to get tricky.
As a side note, the concept of using a different framework for small devices (ie switching to jQuery Mobile), is probably on the wane. The last while I've been advocating rather using the Desktop framework in all cases, and then using an appropriate style for the size of the screen.
I've discussed this a couple times in the last 6 months on the user group webinars, and it seems to be working well that way. I can forsee a time when the jQuery Mobile support is deprecated in favor of a more inclusive desktop framework.
cheers
Bruce