I'm still using my original iPhone 4.
But, my home button has gotten janky. I usually just use the soft-home-button that you can pin to the screen, but that is a bit of a hassle too. I looked into replacing it, the part is ~$5, but you gotta tear the entire phone apart from the back to get to it!!! Thanks a lot, Jobs.
My speakers also don't work any longer. Seems to most likely be because it always thinks that I have headphones plugged in, when I don't.