Here's a simple virtual dice application for mobile (touch) devices. If you ever forget your dice, just open the widget and start gaming! (No, I don't think apps can ever replace dice. They just don't have the feel. I'll most likely use this tool when trying to create adventures from helper tables when sitting in a bus on the way to work.)
If you like this web application, please share this page & send a comment. If the tool sees use, I might develop it further to give you more complex rolling options (but still keep the simple interface).
Also, I haven't been able to test this on various devices, so if it works really badly on some phones/devicses please let me know.