Mobile Phone provider Vodafone offers the Jablotron GDP-02 GSM desk phone in Germany.

I have now idea why someone would need a mobile phone in the form of a standard desk phone, but here it is. Vodafone offers this phone for the at home service option. This service is for people who do not get or want a broadband connection via a wire and are fine with the mobile network.

The only good feature is a small QWERTY keyboard for SMS, but if you have to write SMS novels get yourself software for your PC to send those out. The Jablotron GDP-02 measures 240×240×100mm and weighs close to 1kg.
More details on Vodafone (German) and on Heise (German).