Something all of you will have to do at some point is replace the cell phone you currently have (or, if you do not yet have a cell phone, to purchase one). If you walk into a cell phone shop, you are going to be ripped off 99% of the time. Here's why:

1) If you buy from a contract-carrier, they will upsell you. This can happen in a variety of ways. For starters, they will always recommend a flagship over a mid-range or lower-end phone even if it's far more tech than the consumer might need. More than that, if the phone model has options like expanded storage or RAM, expect them to upsell you on the most expensively-configured model. (Looking at you, iPhone.)

2) If you buy from a prepaid-carrier, they'll give you a phone for 60% of its value, but you cannot take it to another network. Ever. Now, they say you can unlock the IMEI after 12 months, but that's only one half of the equation. If the carrier you are going to does not accept the IMEI of the prepaid phone (and in many cases, they will not), your phone becomes a paperweight when you ditch the company.

So, what is a consumer to do? Simple: purchase an unlocked phone! When you buy a phone direct from the manufacturer or one of their certified resellers, you are getting a phone at a fair price which can then be taken to any network of your choosing (with certain restrictions based on the antenna bands of the model). This even opens you to phone models you would never see in a cell phone store. For example, did you know Sony makes their own phones? They do! And you can buy one!

So, this entire thread is going to talk about the many considerations when buying a phone. To me, phones have always been a bit of a fashion accessory while also being a vital tool for information, so I'll purchase a new one every 6-12 months, pop my SIM card in, and be good to go. My old phone will go either to a family member or a friend who needs one.

I'm making this a mission because I want y'all to familiarize yourself with this information so that you can share this information with others. A lot of good phones go unsold, and that's bad for the environment. Additionally, phone carriers are some of the most corrupt entities on the planet - with a fair share of horror stories to go around. They should have ZERO right to control the phone you use and pay for with your own money (especially when they try to force their logos onto every square inch of each one they distribute). So without further ado, let's get started! (Several posts incoming.)

Part 1: Research!
When the time comes for me to purchase a phone, the first thing I do is go to a database on all smartphones currently in production. GSMArena is a place where you can look up phone specs and read reviews on just about every major phone that has come out in the last 10 years. Here are the things you need to know:
1) Network: We can assume that most phone carriers around the world have moved to LTE by now and have begun shuttering their 3G networks. (Though if you do still require 3G as a fallback for voice/SMS, just know that most companies around the world use GSM, while some North American companies like Verizon and Sprint still use CDMA). LTE comes in a variety of antenna bands, so it's important to familiarize yourself with the antenna bands of the network you are on. For example, AT&T Wireless (in the USA) uses LTE bands 2, 4, 5, 7, 12, 17, and 66. Any phone you buy needs to have these bands for an AT&T SIM to work.
2) Launch Date: Knowing when the phone was released gives you an idea of its market status. Phones tend to drop in value one year after launch because they are replaced by new models, but the hardware and software can still be quite viable. You can even sometimes find factory-sealed models up to two years after their release.
3) Body: You want to know how big the phone is going to be, what it's made of, and how durable it is. Some phones are fully water-resistant, while others are merely splash-resistant. Additionally, some phones come with more than one SIM card slot.
4) Display: Screens comes in two flavors - LCD and OLED. LCDs are not as color accurate or battery-efficient, but they tend to be more reliable. OLEDs (especially older ones) suffer from screen burn-in if the display remains lit for a significant length of time. That said, only OLED screens can support functions like a hole-punch camera or under-display fingerprint reader. Display resolution is usually going to be 720p (HD), 1080p (full HD), 1440p (2K), or 2160p (4K). Some phones have an increased refresh rate (90-144Hz) making them buttery-smooth during things like gaming.
5) Platform: In most cases, it's iOS or Android. Your OS version should be no more than 2 generations behind, so try to find a phone where the OS version is upgradeable. CPU/GPU is its own at-length discussion and will be covered in another post.
6) Memory: Some phones come with a MicroSD card slot, and some do not. On-board storage will always be partially used by the operating system. For example, a 32GB phone may only have 16GB of space for files and apps. RAM-wise, iOS requires less RAM than Android due to kernel-level optimizations. In these modern times, 3GB is the bare minimum for Android, with 4GB or higher recommended. You are better off getting a 1GB phone running Android Go than a 2GB phone running Android proper. Trust me on this.
7) Cameras: Phones can now have up to 5 cameras on the back and up to 3 cameras on the front. More megapixels can be good but only when the phone uses software algorithms to compress the image file into a reasonable resolution with enhanced detail. Otherwise, you will not see an improvement. Bad optimization will ruin your camera experience. Guaranteed.
8) Communications: Your phone will need Wi-Fi, Bluetooth, and GPS. If you want to do mobile payments, you need an NFC chip. For AR and VR, you need a gyroscope. Most phones are shipping with USB-C now, but the 3.1 standard is much faster than the 2.0 standard. Stay away from micro-USB; it is a dead technology.
9) Battery: The more milliamp-hours, the better, but make sure that your device also supports fast charging - whether wired or wireless.

Part 2: Define!
Once you have an idea of what's out there, it's time to narrow down what your needs are. Here is an outline of questions you can use and sample responses.
1) Determine the LTE bands you need. (EX: 2,4,5,12,17,66)
2) Determine the oldest release date you can accept. (EX: 2018)
3) Determine the overall package. (EX: 1 or More SIM, Water Resistant, Gorilla Glass 4+)
4) Determine the display size/quality. (EX: 5.7"-6.2", 720p+, LCD)
5) Determine the platform you need. (EX: Android 7.1+, Snapdragon 600+)
6) Determine the memory and storage needs. (EX: 32GB Storage, 4GB RAM, MicroSD Slot)
7) Determine the cameras needed. (EX: Rear Camera 13MP+, 1080p+ Video; Front Camera 8MP+, 720p+ Video)
8) Determine the necessary communications. (EX: 5GHz Wi-Fi, NFC Chip, Built-in Compass, Fingerprint Reader)
9) Determine the battery needs. (EX: Any Capacity, Fast Charging)
10) Determine the price you are willing to pay. ($250 or less.)

Part 3: Comparison Shop!

For this part, you should start hitting up manufacturer websites to see what is on offer, as well as hitting up retailers of unlocked phones (EX: Amazon, Best Buy) to see what they've got. When you've got a few potential picks, compare their specs to the criteria you specified. Let's look at my current phone which I recently purchased (an LG G7 Fit).
1) LTE Bands: All supported.
2) Release Date: 11/2018
3) Package: Dual-SIM, Water Resistant, Gorilla Glass 5.
4) Display: 6.1" LCD, 1440p resolution with ability to drop to 720p for battery efficiency.
5) Platform: Android 8.1, Snapdragon 821 Chipset.
6) Memory/Storage: 32GB Storage (16GB usable), 4GB RAM, MicroSD Slot
7) Cameras: 16MP Rear, 8MP Front.
8) Communications: 5GHz Wi-Fi, NFC Chip, Built-in Compass, Fingerprint Reader.
9) Battery: 3000 mAh, Quick Charge 3.0.
10) Price: $219 (Limited Sale)

Part 4: Purchase!

So, you've come up with a device you want at a price you are comfortable with! All that's left is to buy it. Simple, right? Well, not always. Let's say that you want a phone that costs $600, but it would take you six months to put aside the money. This is where financing comes in. In order to sell high-dollar phones, phone manufacturers often partner with creditors like Synchrony bank. As long as your credit isn't terrible, most of the time they will offer you a deferred-interest credit card. Here's what you need to know:
1) Deferred Interest means Zero Interest - With a Catch. Usually, there is a time limit from 6 months to 24 months. If you pay the entire balance before the time limit is up, you pay no interest. End of story. However, if you fail to pay the full balance before the time limit, you will be hit hard with a backdated interest charge - which can be significant. Do not EVER sign up for a deferred interest credit card if you do not think you can make all payments before the specified time limit.
2) Deferred Interest credit cards help your credit. Receiving one of these cards means it will go onto your credit reports, and as you make payments, it establishes proof of financial responsibility with the Big Three credit card bureaus (Equifax, Experian, TransUnion). When you go to apply for other credit cards, automotive loans, and so forth, that evidence will work in your favor.
3) Deferred Interest cards are reusable. After you have paid the full balance, you can keep the card open indefinitely. The next time you purchase a phone using that card, the deferred interest period begins anew, and you have another 6-24 months to make payments. This also reflects well on your credit reports.
Understand that these are only guidelines, and there is no downside to paying for a phone with cash instead.

Part 5: Recycle!

This is perhaps the most important element of phone ownership. Phones are not easily disposable because of all the rare materials that are within them - such as gold and lithium. Therefore, the first question you should ask is: "Does my phone need to be destroyed?"
99% of the time, the answer is no. The ONLY scenario in which a phone needs to be destroyed is if it was used in a manner where the data on it needs to be eliminated entirely. In that case, you would likely pull the battery and then put the phone in a mechanical vicegrip until it is reduced to dust.
After you have transferred all of your data and your SIM card to your new phone, you can wipe the data off the old phone pretty easily. This is not a complete wipe, but there usually isn't a need for one by most people. The phone can be given to someone else to put their SIM card in (assuming the phone is either unlocked or to be used by someone on the same carrier), in which case the IMEI can be re-assigned, and there are no problems. Alternately, after wiping the phone, you can use it on Wi-Fi only as a media player, in-car sat-nav (with offline maps), or even as a home security camera (with the right software).
Do all of these things, and you'll be well on your way to being an informed consumer and responsible phone purchaser. I will be updating the remainder of this thread periodically to explain more technical things and to answer questions. Also, if you purchase a new phone and have a perfectly usable old one, I implore you to use this thread to discuss transfers of ownership with other members of The Dollars. One person's trash is another person's treasure.

wow thanks a lot for the information