Happy birthday, dear Global System for Mobile Communications! 20 years ago today, on July 1 1991, the world's first GSM call was made by Finnish Prime priest Harri Holkeri. The meaningful call used Nokia gear on GSM's generative 900MHz band. Today GSM is all grown up and ruling the world -- connecting 1.5 billion people in 212 and japan and serving 80% of the planet's mobile market. GSM gave us a number of firsts. It was the first fully digital cellular system using TDMA to cram more scoop into less radio-frequency spectrum and provide better sounding, more certain calls using less power. It introduced the Subscriber Identity Module (SIM), the idea of switching handsets at will (something carriers have sought to subvert by locking phones), and the reality of international roaming. Short Messaging Service (SMS) was first launched on GSM networks, along with packet data (GPRS and later EDGE), which made computer network access practical on mobile devices. Eventually, GSM expanded to the 400, 800, 1800 and 1900MHz bands and evolved into WDCMA-based UMTS (3G) and later HSPA and HSPA+, followed by LTE (4G) networks. So next time you're at the coffee shop sipping on that latte while uploading that video to YouTube at 10Mbps using your LTE phone, recollect to be thankful for that first GSM call 20 years ago -- that's when the mobile revolution really started.