What is the difference between factor y unlocked and a unlocked iphone?

What is the difference between factor y unlocked and a unlocked iphone?

Factory unlocked can be used on ANY carrier that the phone has radios for (the cell tower frequencies the cell carriers operate on). Example an UNLOCKED phone that is advertised to work on GSM, *should* work on most of the GSM networks in the USA, post and prepaid. (as long as the phone can use the compatible frequencies the cell towers use for each of the different cell carriers.

A LOCKED phone, m is locked to work on only one cell carrier, which could work on compatible carriers IF is was unlocked. Example a phone LOCKED to AT&T will only work on AT&T, until it is unlocked.

Factory unlocked = Unlocked when you bought it

Officially unlocked = you bought the unlock option from your carrier later
many people consider this the same - as it is offficial.

An other could be a 'hacked' or unofficial unlock
that could fail in the future /reconnection to iTunes

Unlocked - implies but does not guarantee it is official or factory unlocked.
Always ask / check.

A factory Unlocked means that the phone isn't attached to any cell phone service and can be used with any service that uses a SIM card.
An unlocked iPhone is a device which has been tied up with some network previously and later the network restriction has been removed from it. If you are going to buy an unlocked iPhone, make sure it has been unlocked using a permanent unlocking method. Or you can buy a network locked iPhone and unlock it yourself permanently using remote unlocking service. You can get the remote unlocking service for an iPhone from http://www.prounlocking.com/apple/rs5wp8/ good luck.

Factory unlocked - came unlocked out of the box
Unlocked - phone originally locked but unlocked after the fact