Heh. I actually finally got rid of my iPhone 4 for the Samsung Galaxy S4.
So I guess I got you beat there because I recently upgraded from an iPhone 3G to a Samsung Galaxy Note 3. (similar switch as you, but from an older model to a newer model.)
I briefly considered the iPhone 5c because, well, it comes in pretty colors. Yes its a silly reason, and you can get cases for most phones to get the color you want, which is why this wasn't a huge pull. Still, it seems silly you only get white and black all the time.
I've had an iPhone for -years-. I really liked it at first, but over the last couple years I've found it very irritatingly slow. And there is no reason it should be even if it is older, since I only used it for fairly simple stuffs like checking bus times or email. BUT there was a bug in firmware version 4 that caused major slowdowns. Like, you are trying to type something and only one character would show up, then, and I'm not exaggerating, like half a minute later the rest of what you typed would show up. So frustrating.
And guess what? Apple never bothered to fix it. That was the last update to the firmware. After that they stopped supporting that model. And while I think it's understandable that they'd stop supporting their older phones, they could have at least reverted to the last known good firmware before dropping it. Ultimately, that's what made me decide to look elsewhere and try a different kind of phone.
