In the following video https://youtu.be/CUUnnf_gX1s?t=46s you'll see that when the button is tapped, the screen "tears" when the device re-renders its display. I doubt this OS was using the GPU to render and composite its components to the display. It seems more like it is software rendering the UI then passing the entire buffer to the GPU for display.
Notice also that the scrolling on the device is line-by-line rather than per-pixel. It's done to minimise screen redraws but it is exactly the opposite of what made the first iPhone so pleasant to use. The only one-to-one interaction in the Nokia 7710 video is the little sliders being moved by the stylus, but they too flicker when redrawing.
My point wasn't really about whether a phone supported OpenGL. I was pointing out the software design of the graphical compositor used to render and animate the UI, and how every small decision was made in favour of prioritising an immediate reaction to human input.
The only reason I mentioned the iPhone's meagre mobile GPU was to emphasise how iOS was able to produce such low-latency and smooth performance from very low powered hardware.
Yep—smooth scrolling was a famous obsession of Steve Jobs that was emphasized in just about every Apple product where it was feasible, the idea borrowed from one of the fated PARC demos. Little things like this go a long way in building a sense of symbiosis between user and device.
Although I do concede that if it wasn't for iPhone's success, OpenGL ES would probably never had taken off, as Symbian was one of the very few mobile OSes that had some flagship devices with hardware support for it.