Not sure which one you are referring to. Perhaps the Nokia 3205, a very youth oriented phone. It has user-customizable faceplate so could have diamonds or almost anything else.
go to sprintpcs.com/support/guides/allPhones.html for a picture
hmm perhaps it was only available in Australia? it was marketed towards women, it was a red flip phone with a clock on the front with diamonds around the edge. it also had a mirror inside it. i believe they also brought out a champagne coloured one a couple of months later. (they don't make the phone anymore and i'm trying to track down a used model, which is hard without the model number!!)
