Even though the 5510 was revolutionary, it technically wasn't the first phone with an MP3 player. The Siemens SL45 introduced this feature almost 4 months before, in August 2001! : r/vintagemobilephones
AC adapter / charger suitable for Siemens SL45 - Universal Rapid Charger - BatteryUpgrade
All-O-Matic SL45 DC Slide Gate Opener (Limited Time Sale) – Elite Gates