Almost all mobile devices support (name a phone and it supports OpenGL 1.1 ... even other portable devices stuff like the Pandora [if anyone still ever thinks of that device] and well ... the PS3 which isn't really a mobile device) and almost all the popular mobile devices currently sold (as opposed to a couple of years old) support OpenGL ES 2.0.
Official References for OpenGL ES 1.1 and OpenGL ES 2.0:
OpenGL ES 1.1: http://www.khronos.org/opengles/sdk/1.1/docs/man/
OpenGL ES 2.0: http://www.khronos.org/opengles/sdk/docs/man/
[Interesting note: Note in the Wikipedia articles that OpenGL ES 2.0 is apparently the standard for WebGL. And *cough* it won't work on older Intel GMA which according to Wikipedia "In early 2007, 90% of all PCs sold had integrated graphics." because "Many older Intel graphics cards (e.g. GMA950) don't support programmable shaders, so they cannot be used to render WebGL content. " ... ]
OpenGL ES 1.1 does not support glBegin or glEnd or any of the "manual" vertex stuff or glTexCoord2f type of stuff. (Hmmm ... how would, say, Quake animation interpolation look in that. And just by that thought you can tell I haven't poked around at that part of DarkPlaces or FTE or even Qrack for that matter or anything else that uses vertex arrays.)
OpenGL ES 2.0 does not support any of the "immediate" functions like glPopMatrix and you don't use glRotatef or glScalef or glTranslatef apparently. *sniff* I understand the advantage of the "fixed function pipeline stuff" but I kinda have always liked the ability to use glPushMatrix to offset from the "camera" and then draw something and use glPopMatrix to restore everything back to how it was. In some ways this is preferable to ... I guess ... having to calculate your own matrix as Spike has described how it works. I suppose this disallows some of the other matrix fun too (in favor of having to wrap your head around some complicated calculations.) And I guess OpenGL ES 2.0 hates quads.
[I bet 3 months from now I'll probably look back on these things with 2.0 as trivial ... but today it seems like a headache ...]