WebGL is not supported by any mobile browser yet (http://caniuse.com/webgl)
(edit: it seems that Blackberry Browser and Opera Mobile support WebGL. My bad, but it is not possible to use these browsers on iOS)
Firefox for Android and Chrome for Android support it, according to that table (unless your driver is blacklisted).
CanIuse is incorrect. Firefox on Android has supported it for years. Chrome added support recently.
That being said it is easy to OOM mobile browsers with textures.
Doesn't work for me in Mobile Safari or Chrome on iOS.
Chrome in iOS is just using UIWebView to render the webpage, so it is still Mobile Safari, only with the services provided by Google.
If you can read caniuse's table, you'll see that WebGL's actually supported on mobiles. You can get a more quantitative view from http://webglstats.com/ if you'd like.
Blackberry has been pretty active in the WebGL community. I was actually surprised and impressed with the performance the first time I saw a demo on the Playbook!
WebGL works in all browsers on desktop and on most smartphones/tablets - except on iOS platform (Safari, Chrome) as Apple has disabled the support [1].