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
Siemens C45- Blue Mobile Phone Untested | eBay
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3RV2042-4JB10 SIEMENS Circuit breaker size S3 for motor pr..
SIEMENS SL45 USER MANUAL Pdf Download | ManualsLib