Posh Micro X, claimed as the "Smallest Smartphone in the World". This has been on sale for some time and gets reasonable reviews on Amazon.com, typically commenting it is adequate given the size. The Jelly appears to offer upgraded electronics and software compared to the Posh and better compatibility with global phone networks.
Motorola A760. This protects the screen when closed (but with the display visible through a transparent window). You could then answer a call by opening the flip and end it by closing. The cover has channels to take the sound from the speaker in the body of the phone up to your ear, making it more comfortable to hold.