Can not enable LTE/4G on iPhone 5S unsupported carrier

Might I point you to http://www.apple.com/iphone/LTE/. This document shows the specific models, AND the supported carriers. If your carrier is not supported, you likely cannot access the feature at present.

Your carrier supports the other fully unlocked device and has a carrier settings file that contains the necessary configurations they require for LTE. And the SIM for the phone also is configured to work with their LTE settings.

Since they are not an authorized Apple carrier (and that does not really require any extra money on their part) then they are not able to provide a carrier configuration file that is installed in the iPhone. As I said above you are able on an unlocked phone to change the APN settings on your iPhone. Call your provider and get them to provide you the necessary settings for their system. Also ask if they have a compatible nanoSIM.

I totally agree with you. It is something to do on on Apple's side. In my country the apn settings differ by only 2 ways. Either it's prepaid or postpaid. So the apn is not depended on phone we are using. This is what my carrier says (which is unsupported by apple) when asked about getting 4G LTE on iPhone 5.

"Not at the moment; no. Apple has not opened LTE services to Sri Lanka. If/when it does, users with Apple devices operating on 1800Mhz Band 3 should be able to enjoy 4G."

This is directly from carrier support.

When I use the apn for mobile broadband, an LTE enabled android device it works automatically. But on iPhone 5 only upto 3G works. But somehow 3G works on my iPhone without entering the apn while mms and tethering requires apn.

Talk to your provider. They do not have to be an official provider they just have to make the requisite settings known to you and then you can manually change the APN settings on your iPhone. They would also have to release a nanoSIM that would be compatible but they do not have to become an official Apple carrier to do that either.

You are stubborn aren't you? Apple has locked NOTHING on that phone. Nada. Is there a supported carrier where you are? Use their system and it will work just by inserting their nanoSIM. Go to 15 other countries and you can put in a compatible nanoSIM from a supported nanoSIM and it will work right away. Why? Because when you put in the compatible nanoSIM and connect it will update the carrier configuration settings.

Since you are using a carrier that is not affiliated with Apple there are no such settings in the configuration file. You have to manually add them yourself. And your chances would be much improved if you had a compatible nanoSIM (not cut down microSIM) to put in the iPhone.

LTE is carrier specific. Different models access different bands. If your carrier is not a supported carrier that offers LTE, then you won't be able to use the feature.

You will probably have to wait until your carrier (and it is them, not Apple) release a carrier update through Apple.

Is this on T-Mobile USA or somewhere else?

Yes, that would be adding APN settings. Again, contact your cell provider, or go to their website, and someone has probably posted the settings necessary.

What was the tweak that you did.

Apple can only include the configuration settings for those cell systems that they do business with. If the cell carrier does not send the requisite APN settings to Apple there is no possible way Apple can include these in the iPhone that is sold to you. They have to be added manually (or tweaked or whatever you want to call it).

If Nokia/Microsoft is not an authorized phone on your carriers system then an unlocked phone from them will also not work UNLESS you tweak the APN settings to make it work. Your iPhone 5 was tweaked to make it work.

No, you won't get LTE on any unsupported carrier. That's just the way it is.

but my carrier has a contarct with apple and they dont let lte 4g and say its apple carrier update

AGAIN, your carrier is probably an official carrier for Samsung so the carrier settings on the Samsung are predefined to work with their system.

Cut down microSIMS are tricky and may work in one phone while failing in another. Best to use a nanoSIM designed for your phone. Call your carrier and ask them what settings you need to change in your APN file and try again. Or better yet return the iPhone and use a Samsung Galaxy S4.

Then it's more than likely up to the carrier to have that option enabled from what I've read on it.

You don't have to wait, as I said go to the user support site for your carrier and someone will have posted them. Or use Google and search for them.

Who is the carrier and where?

That's how I got to this page was a google search. There is no way to enable LTE without a JB, I just don't understand why this has to be so difficult.