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 Minister Harri Holkeri. The historic call used Nokia gear on GSM's original 900MHz band. Today GSM is all grown up and ruling the world -- connecting 1.5 billion people in 212 countries 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 information into less spectrum and provide better sounding, more reliable 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 internet 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 byLTE (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, remember to be thankful for that first GSM call 20 years ago -- that's when the mobile revolution really started.