Does unlocked on a iphone means in no service?

So i want to switch to t-mobile. I'm buying an used att iphone 4. And i just want to put the sim card something like that. And in every page on tutorials it says it needs to be an att iphone unlocked. But i don't know what unlocked means. Does it means like the phone is from the company att but like in no service? Or what does it means?

Unlocking is when the sim gets unlocked so the phone won't be locked to one plan and you can use whatever sim you like.

The used phone must be from a different network or its a face phone, go to a phone expert and see if they can help i always buy new phones i find them alot easier and if you have problems you can just go to the people yoy bought it off as if you have s receipt you can slways show it and they know you arent lieing

An unlocked iPhone means it can be used on ANY cell network, not just Verizon, ATT, or Sprint. There are a million videos giving in-depth tutorials on how to unlock an iPhone based on your firmware version. An unlocked iPhone will have whatever the service of the SIM card is (ex. If you put in a T-Mobile sim, the phone will have T-Mobile service). Unlocking your iPhone is a completely legal process, and is a great way to unleash the true power of an amazing device.

If you want to get fancier, get into the world of jailbreaking too, lots of amazing stuff to do. Google "why should I jailbreak my iPhone" and read up on some of the articles.

Unlocked means that the iphone 4 can be used with any other provider that uses sim cards. Atandt phones come already LOCKED to the company, so for you to do this you need to pay someone to unlock it. Or already have an unlocked iphone 4.

At this point you can simply put in the sim card.

What I advice you to do is go to wallmart and buy a cheap 20 dollars STRAIGHT TALK phone that has and atandt sim card in it. You can ask them which ones have it. Then use that sim card cut it down to use on iphone 4 and then use the plans from straight talk. For 45 bucks you get everything unlimited.

I will be doing this on my iphone 5.

Unlocking means that you have the iPhone unlocked by a factory unlock provider like iPhoneUnlockedCheap.com or any other unlock provider. Once you do this, it will allow you to use any GSM sim card in your iPhone worldwide (not just AT&T which it was locked to originally). Hope this helps