I found my old Huawei U8650 in the closet. It works, I just need to replace the battery. It has android 2.3.5. I was thinking to use it primary for reproducing music for my bluetooth speaker and for mail, calls and sms - my second SIM card. Is it possible to put some other android version that will boost up a speed a little bit? Thank you.

https://www.gsmarena.com/huawei_u8650_sonic-4205.php

You maybe able to find a customOS for it, that is a port of the latest version of android. But chances are that maybe slim as that device was not exactly mainstream.