The Siemens SL45 from 2001 was the first phone to have a card slot for storage and also the first to feature an MP3 player. It came with a 32MB (megabyte) MMC card and a pair of stereo headphones. Unfortunately, those used a proprietary COM port to connect to the phone (as did many phones later on). The familiar 3.5mm audio jack didn't arrive on the scene until 2005 and it wasn't alone. We picked the Top 50 phones (by user interest) for each year and counted the number of audio connectors. Between 2007 and 2009 there was a brief challenge by the smaller 2.5mm jack, but that fizzled out...
Source: https://www.gsmarena.com/counterclockwise_the_35mm_audio_jack-news-28302.php
