Active Edge, which LG originally came up with and that Google adopted with the Pixel 2. Of course they dropped it after a few devices.

It was basically a button/key press that you could configure to trigger actions by firmly applying pressure with you hands around the lower third of your phone. It gave a very satisfying haptic vibration response based on the amount of pressure you applied and you could even set the amount of pressure until it was triggered. It had something magickal about it.

If you're interested in the tech: https://www.idownloadblog.com/2017/10/19/google-pixel-2-teardown-ifixit/

Removable battery and LED notification lights.

I miss the gboard of 5 years ago when typo correction was spooky good.

I miss uploading my own songs to Google music.

I miss easily flashable bootloadera and roms.

I miss the three virtual navigation buttons.

I miss setting different notification dot colors for different apps.

I miss setting different notification sounds for different people.

Honestly, I miss my hardware keyboard and not giving up so much screen real estate while typing.

I miss the times when different phones had character. Even phones of the same company looked completely different:

Now it’s just the same rectangle stretched different ways and maybe different color sides.

I miss the notification LED on older Galaxy phones.

Physical keyboard. I miss touch typing one handed.

The back fingerprint reader used to have gestures, so swiping down on it could for example open the notification shade. Was really good for not having greasy fingerprints on your screen

I kinda miss flip phones? These days phones are too big for my hands and pockets. I find myself buying cheaper phones just so it's a little smaller.

Yet another of Google's discontinued pet projects with tons of potential but that that they quickly lost interest in, my trusty (now officially unsupported) Pixel 4XL has a Soli Radar sensor that I'm going to miss when I finally break down and buy another phone.

It is so nice to be able to just wave generally in the direction of my phone to do stuff. I use it all the time when I'm driving to skip songs, or repeat the last song, or pause the music, etc. without taking my eyes off the road. It really is a shame to me that they threw a bunch of money at a legitimately cool project like that, and then seemingly just abandoned it entirely.

Add it to the list, I suppose.

I miss the function when the phone would stay tethered to its cable at home where it wouldn't bother me all the time when I was out and about.

Nokia phones in 2000 could record your voice for any command you wanted. The voice command reliability of those phones is beyond superior to what is offered by today's voice assistants.

Samsung Galaxy Note 3 had a feature in the camera app which would take several pictures in a row and you could then choose the one with best quality. Extremely useful feature especially in low light. I'm sure there's an app out there that can do this but I can't find one.

I'm not sure exactly what it was called but any time you took a photo with a Note8, it was always taking photos from right before to right after the photo. This resulted in much fewer garbage photos because a few frames before or after the shutter was pressed would be a better photo, one that is not blurry! Now instead of a useless photo, I would have at least something workable. I have not seen that on any other phone with this feature, including my current one.

Welp - I'm thoroughly convinced to never upgrade from my BlackBerry Key1. I will hang on to my multi-day battery life, 3.5mm headphone jack, keyboard, notification LED, fingerprint reader, and cheap, replaceable parts till phones stop being a fucking thing.

I recognize this list of "Gone for everyone but me" may not be perfectly in the spirit of this question, but all the same: Thanks everyone! :D

Physical keys that you had to type multiple times to get letters. I could write a whole text message with my hands in my pocket.

The IR blaster on my galaxy s6. Not the most used feature, but when the Air BnB didn’t have all the remotes it was a life saver.

Dunno if this counts, but screens that fit in my goddamn pocket.

Not really a feature. But I really I wish I could upgrade my phone. Like, get a new camera with better quality or a new battery with higher energy density in an older phone. Stuff like this.

Phones: ability to throw it on the ground without anything bad happening to it.

Other: software that you could just own.

SensMe in Sony and Sony-Ericsson phones and players. It was the tool that analyzed your music collection and sorted it according to energy, mood and tempo.

The best variant was on the later products whey you had a list of channels representing either moods/styles (Energetic, Emotional, Lounge, Dance etc.) or time of the day (from 'Morning' to 'Midnight'). The results were very good, especially for the time channels (except the morning) which were perfectly fitting the mood and pace of times of the day, much like Indian ragas. It really felt like your personal radio stations, freeing you from having to make playlists by yourself ever again...

It was discontinued in 2010s because of declared low adoption by users according to some obscure internal studies :( I've been dreaming of replicating it using Python ever since, but never had time to do a proper research.

Predictive text like my Nokia's T9. It knew how English worked and what the probability of a word in context was.

Now it's all: "the same time and consideration and I are going to be a good time to get the latest Flash player is required for video playback is unavailable right now because this video is not available for remote playback is unavailable right now because this...."

Keyboard and the ability to physically close the phone to turn it off/sleep/hangup.

The knock code really was so convenient and safe. No way for other people to see it.

I was an avid fan of LG phones, especially the G series. I mean yeah, some features were kind of pointless (G5 Module??)

The Snake game you could play on push button phones. Oh my goodness.

I had a 2nd Gen moto x. It had proximity sensors around the screen that allowed you to make gestures over the phone to do things like check notifications, pause music, dismiss calls, etc. They also offered a lot more customization options than any other phone I know of. Mine had a leather back, which was available in a few colors. They also had several options for wood backs. It was a really nice phone and I was sad when it died.

Not phones, but TVs. My first flatscreen tv(not a smart tv yet) had a picture in picture mode, so I could play games while my family watched TV. That was nice, but it seems to have just vanished as a feature in modern TVs.