How you know when an iphone can be unlocked?

You will need a gevey sim, a computer that you can download software onto ( you have admin privileges). Also you will need a certain baseband ( labeled modem firmware ) to unlock To find this, ask the seller if they will let you have some "hands on time" with the phone before you buy it. Then, from the settings app, go to General>about and scroll down to modem firmware. This is your baseband. Here is the website withe basebands and details http://www.ijailbreak.com/cydia/ultrasn0w-fixer-for-ios-5-1/ Also, scroll through the apps the phone has. If it doesn't have an app called Cydia or Rock store, than it is not jailbroken.

It's GSM Network Locked Phone means it can be unlocked.It's CDMA Network Locked I-phone 4 means you cannot Unlock it from network lock....Then after Unlock it you can use any GSM Network Sim card...You cannot use any CDMA Network Sim card....It's Unlocked I-phone 4 means it will accept any GSM Network Sim card..It's Locked Phone mean it will not accept other Network Sim card ...Say Invalid Sim like that.....You can get the Remote I-phone 4 unlocking service from http://www.mobileunlocksolutions.com/apple-iphone-4/rs1wp9/ and unlock it easily.I have Unlocked from T-Mobile Network Lock United Kingdom(UK).

iphone 4 can only be unlocked if its on baseband 1.59.00 or the 2 year contract is up and att unlocks it. if you need an unlocked iphone 4 email i have em for sale or trade.