Asked this lady to lemme take pics of her keitai (mobile phone) - spotted it when she was taking pics of me in armor ^^;
This type of keitai is known as "Decoden" [デコ電] (also spelt as "Dekoden") which is short for "Decoration Denwa" - "Denwa" meaning "Phone."
Many folks buy these shiny jewel like plastic parts at places like Dekoden.com and decorate their keitai themselves. Some places sell sheets that come with decorations on them already which you can just stick on your mobile - some at King Deco from about 4,000 yen.
And then there are places who will make to order.
And its not just keitai that folks decorate - check out the NDS decorations below - and the G Shock...
And a video below of a charisma decoration artist showing off some of ther Nintendo DS and keitai art.
Other images from:-