The Jablotron GDP-02 GSM desk phone would fit your needs perfectly. The phone features a small QWERTY keyboard for SMS, measures 10x10x4 and weighs 2.2 pounds.

For sturdy utilitarianism, there were few designs better than the Western Electric Model 500 desk phone. The 500 did one thing and did it well, and remained essentially unchanged from the mid-1940s… ...

I know this looks more like a standard issue desk phone with an Android device built in, but I assure you it's the other way around. ... The Smart 5500 has support for 2G GSM and 3G CDMA networks.