What is Unlocked or Locked iPhone?

I see different models have different prices. I want 2 ask difference between Locked iPhone, No contract iPhone, Locked carrier and Gsm or cdma iPhone.

But, if i'm buying AT&T iPhone and unlocking it with R-Sim 9 pro, then will i be able to use it worldwide carrier?

Added (1). what about this phone - https://www.google.com/...CGwQpiswAA

First, let's deal with GSM vs. CDMA. If you're in the United States (and it appears you are), different carriers use different radio technology for their phones. AT&T and T-Mobile use GSM, which is generally the worldwide standard. So if you're going to be using your phone while traveling abroad, you'll definitely want a GSM phone for maximum compatibility with foreign SIM cards. Verizon and Sprint use CDMA. Some of their phones also have GSM radios which are inactive unless you're roaming (i.e., traveling in a foreign country), so they can in fact also be used internationally, but you have to specifically make sure the phone you're buying is "global ready." So, best to stick with AT&T or T-Mobie, then.

As for locked vs. Unlocked, this refers to whether the particular iPhone is "locked" to a particular carrier. For example, if you buy at iPhone 5S for $199 on a new 2-year contract with AT&T, that iPhone will only work on AT&T until you've completed your two-year commitment, at which point you can ask AT&T for what's called an "unlock code." You can then bring your phone to another GSM carrier, such as T-Mobile, if you wanted to switch. The benefit for you is a much lower initial cash outlay for your phone. The benefit for the carrier is that they have you as a customer for at least 24 months, guaranteed.

An unlocked phone, which as you've seen is much more expensive, is NOT locked to any particular carrier. This is the phone you want to get if you don't want to be tied down by a contract, you tend to move a lot and need to switch carriers (though AT&T and T-Mobile have coverage pretty much nationwide), or if you want to use a prepaid, no-contract service plan. It's also the phone to get if you travel abroad a lot, as you can simply swap out your US Carrier's nano-SIM with whatever local carrier's nano-SIM, then swap them back when you return to the US

Generally, most people tend to get a "locked" phone with their carrier of choice and take the subsidy (the lower price).

Hi, to your second part of the question. R-Sim is not good since you can't update the phone. Go for the factory unlock. It is now for around $20 (check eBay and other sites). You would then be able to use any carrier worldwide.

Locked - when the iPhone is able to only work on 1 carrier.

No contract - when you buy the phone, still locked, but not with a contract. Usually people wanting to get a phone but remain on the network.

Locked carrier - same as locked.

GSM - the more popular mobile network standard. Requires SIM cards

CDMA - used mostly in the US on Sprint & Verizon. Does not use SIM cards.

Yes, if it is able to unlock it then you could use it with whatever carrier you want.