Sony's Clie PEG-VZ90 is a palm-OS powered PDA that has a 3.8" 480x320 AMOLED display. In fact it's the first PDA with an OLED display.

OLED type: 

3.8" 480x320 AMOLED

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Cambridge Isotope Laboratories - Deutreated Reagents and High-Purity Gases for OLEDsCambridge Isotope Laboratories - Deutreated Reagents and High-Purity Gases for OLEDs