I like this accessory,you need this for your  mobile phone- “Mathmos Astro Light Charms”. The Charm blinks when cell phone’s transmitter senses a call.
The Mathmos Astro Light Charms is the creation of UK designer Mathmos. Weighing just 15g, these charms are available in two different styles namely, mini lava lamp shape in Blue or Red (the universal symbol of relaxed retro) and the light bulb in Blue or White 

It is useful in the places where one experiences lot of noise. At least, one can see the LED light flashing if one does not hear the sound. Only those who have 1800/1900 MHZ GSM mobile phones can use this.