1. What does unlocked phones mean?
2. If I root my Samsung S4 does it mean it is an unlocked phone?
3. If I root my Samsung S4 will I get more android updates?
4. Before rooting where does S4 communicate/get android latest version? Is it from Samsung or Android?
5. After rooting where does S4 communicate/get android latest version? Is it from Samsung or Android?
6. Is Android updates supplied by Android or Phone manufacturers like Samsung, HTC, Nexus...?
(My thinking is that Android is like Windows, and Phone manufacturers Samsung, HTC, Nexus are like PC manufacturers Dell, HP, IBM)
1. Unlocked phones generally refer to phones that are not carrier branded and come with sim unocked. It is not tied to any carrier contracts, do not have carrier branding on it, and is GSM sim unlocked, so you can put in any GSM sim into it and use the phone (although depending on the region, some phones will not support all the 3G or 4G frequencies required by your carrier).
There is another term called unlocked bootloader, which is not the same as unlocked sim. Unlocked bootloader as I previously said, allow you to install third party firmware/roms onto the phone, and root it. Usually, unlocking the bootloader will void your warranty unless the manufacturer said otherwise. Usually it is easier to unlock the bootloader of unlocked phones than carrier locked phones.
2. No. If you want to sim unlock your phone you can ask your carrier for the unlock code or pay an online service that will sell you the code.
As for unlocking the bootloader, that is more complicated and depend on which device you use, usually you should either Google it or ask at XDA forum. Remember most carrier branded phones on AT&T and Verizon are very hard or impossible to unlock the bootloader. T-Mobile is more lenient.
3. No, read
here to know what root does. The updates are depended on Samsung and your carrier if your device is carrier branded. The companies have to release the software and make it available for the phone.
4. The process of creating a new firmware for a phone by the manufacturers are complex, it have to go through many processes. This chart is a good example:
https://forums.androidcentral.com/e.../HTC-Anatomy-of-an-Android.jpg&token=kZtTjutp
5. The same thing as before, if the phone even allows it. Mainly, when a phone is rooted, once you install an over the air update, if the update work, it will wipe out root, and you will lose root in the process. With Nexus devices, there are lots of checks in the update, so if it detect any changes in the /system partition, which is changed when you root the device, then the update will fail to work and you will soft brick your device (soft brick mean the phone will no longer boot, but you can flash the factory firmware to restore it).
My experience with some Galaxy phones is that it have Knox, which is a Samsung security feature. If you "trip Knox" or make a "flash count", which means it detects you flashed a third image to the phone, it will prevent you from receiving any future Samsung over the air updates. Although you can still flash the firmware manually or you can try to use use Chainfire's "TriangleAway" method to disable that flash count.
6. Google Nexus devices get update directly from Google (unless it is locked to a carrier). Unlocked carrier-free devices get updates from the manufacturer. Carrier branded devices get updates from the carrier. See the HTC chart above.
I forgot to mention, aside from Nexus devices, there are also "Google Play edition" devices and "Android One" devices. These two aren't Nexus devices, but they use stock Android and will receive updates sooner as well. Nexus and GPe device can be purchases on the
Google Playstore, Android One are affordable devices for emerging markets like India. Also it seems like the concept of Google Play edition are dying or not been very popular with the manufacturers, so there aren't many available anymore, also they tend to be overpriced imo.
Also, some manufacturers also release version of their phones called "Developer edition", which will allow you to unlock the bootloader and not lose your warranty, but they also cost more than the regular version.