Do mobile phone browsers support 24-bit PNG transparency?

I know only MSIE6 (out of generally used browsers) doesn't support 24-bit PNG transparency on the desktops but I'm not sure about mobile browsers.

Is there a good reference for what mobile browsers support (CSS3, Javascript, etc)?

Do mobile phone browsers support 24-bit PNG transparency?

The most common ones do: http://caniuse.com/png-alpha

Provided that you only care about (desktop browsers plus) iOS Safari/Opera Mini/Opera Mobile/Android Browser, you can use http://caniuse.com/ to look up the support for many different features.