I have a 2002 E320. Call these guys
https://www.beckerautosound.com/

Send in your radio and they will add a connection point to plug your phone in. I

I added this for hands free. Works great.

https://www.google.com/search?q=mpow+bluetooth+4.1+receiver+with+built-in+noise+isolator&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari#lbl=OVERVIEW&pie=plaji-i

I think all together it was less than $200.

Most stereo shops wanted to start over = $$$

Good luck!