This has to be one of the smallest mobile phones we have seen here at RoboXpress, the Simvalley PICO RX-80, which measures just 1cm thick.
The Simvalley PICO RX-80 is about the size of a credit card , and it features a 1.2 inch LCD screen with a resolution of 96 x 49, the phone itself measures a tiny 50 x 800 x 10mm.

Here are the specifications:

• Mini Dual-band phone for GSM 900/1800 networks
• Without subscription and released: Simply insert your SIM card and released without subscription: Simply insert your SIM card
• LCD 1.2 “(96×49) LCD 1.2″ (96×49)
• Backlit buttons and display Backlit screen and keys
• Features: reminder, hidden identity, speed dialing, keypad lock, alarm Advanced Features: reminder, hidden identity, speed dialing, keypad lock, alarm
• Li-ion battery, autonomy 90min talk and standby 100heures Lithium-Ion battery, autonomy 90min talk and standby 100hours
• 32MB Internal Memory 32MB internal memory
• Size: 50×80x10mm, format card Size: 50×80x10mm, format card

The tiny Simvalley PICO RX-80 mobile phone is available from Pearl Diffusion (French) for about 18 Euros, about$25.