This document discusses the history and rise of mobile phones and their impact on user behavior and search engine optimization. It traces the evolution of mobile phones from their invention to the development of smartphones and ubiquitous internet access via mobile devices. It notes that users now spend significant time on their phones and are heavily dependent on them. The document also summarizes Google's plan to transition to mobile-first indexing and the potential impacts this may have on websites that are not optimized for mobile or that have separate mobile sites. It provides recommendations for site owners to test their sites and prepare for the upcoming changes.