The Nokia N810 seams to be a great mobile phone. It's linux-based and it runs a Debian derivated OS, Maemo, with a custom user interface built with the GTK-based Hildon framework.
The N810 supports WiFi, a four-inch touchscreen with an 800x480 resolution, Bluetooth, and VoIP via Skype, GPS and a slide-out keyboard.
But one of the greatest features is the support of the Flash Player 9 as well as PDF documents.
This means that you can launch Flex applications on the N810 phone.
If you want to read more have a look at this detailed review of the Nokia N810.