My current phone is an old HTC Desire; I’ve given it a new lease on life by installing a (larger, heavier) 3Ah battery and upgrading to Android 4.0 (Ice Cream Sandwich).
The battery upgrade was a little fiddly as I bought a cheaper kit on eBay (as my Trinidadian grandmother says: “good ting no cheap, an’ cheap ting no good”). The replacement case back had no covers over the camera and flash holes. I managed to remove the flash cover from the old case and fit it to the new unit, but I broke the camera cover. Instead, I used a small piece of clear plastic glued in place; this is acceptable for the moment but I’d like to replace it with glass in the future.
I’m using the Android ICS ROM from http://www.sandvold.as/. It works well; the latest releases don’t crash (for me at least) and everything seems to work except video recording, which produces videos with low frame-rate and encoding glitches.
Some months after I wrote the above, the phone died, and I replaced it with an HTC Desire X on Armin’s advice.