Iphone G4 how to unlock sim card - Apple iPhone Smartphone

Make Sure your iPhone asking for sim unlock code after insert a non accepted sim card( For Ex. if you are using AT&T sim insert the T-Mobile sim in this)
If yes then follow the steps below:
go to the www.unlockninja.com and select as per your requiremnet
Brand Name:-
Model No or Name:-
Country from The Phone Purchased:-
Network on which The Phone Is Locked:-
Mail ID:-
place order to unlocking confirmation at https://www.unlockninja.com/unlock-apple+phone and wait for the giving time that is 30 min to 2 days
You will confirmed via mail as the phone has been unlocked. Then you only need to follow the steps below:
How to fix sim lock in apple iPhone

How to Unlock the Apple iPhone 6 after getting the confirmation as Unlocked
-Install the last version of iTunes on your computer.
-Make sure your iPhone is updated with the lastest version of iOS.
-Switch ON your iPhone 6 with a SIM Card from a non-compatible network.
-Connect your iPhone 6 to your computer using the Original USB Cable.
-Launch iTunes andwait until iTunes detect your iPhone 6.
-Now disconnect your iPhone 6sand reconnect it after 10 seconds.
-Your iPhone 6 is now Unlocked!
Note:-In the unlikely event that your iPhone 6s is not unlocked, please restore your device following the official guideline from Apple - https://support.apple.com/en-us/HT201252

Unlock your apple iphone 4 and use any other carriers sim card
To unlock your apple iphone to use any sim card, you need to get the unlocked confirmation from apple by using any unlock code service provider.After getting the unlock confirmation you need to use i-tune to unlock it
here is the direct link of service provider to get the unlocked confirmation
How to unlock iPhone Factory Unlock iPhone

After getting the unlock confirmation you need to use i-tune to unlock it as below:-
How to Unlock the Apple iPhone 6 after getting the confirmation as Unlocked -

-Install the last version of iTunes on your computer.
-Make sure your iPhone 6 is updated with the lastest version of iOS.
-Switch ON your iPhone 6 with a SIM Card from a non-compatible network.
-Connect your iPhone 6 to your computer using the Original USB Cable.
-Launch iTunes andwait until iTunes detect your iPhone 6.
-Now disconnect your iPhone 6sand reconnect it after 10 seconds.
-Your iPhone 6 is now Unlocked!

Note:-In the unlikely event that your iPhone 6s is not unlocked, please restore your device following the official guideline from Apple - https://support.apple.com/en-us/HT201252

To use any SIM card with your iPhone, you have to unlock your device and not your SIM card. You can unlock an iPhone using remote unlocking service. You can get the remote unlocking service for an iPhone from SuperUnlockCodes.com This method of unlocking an iPhone is safe, simple, affordable, quick and permanent. IT doesn't require a jailbreak too. Good luck.

No The sim card for the older models is not the same size as the new iPhone 5. You can take your old sim card to your provider and they can make you a sim card to fit your new phone.

What kind sim card problem did you face?
Did you mean your iphone doesn't detect your sim card even your sim card present on your phone?
Yes means,
There are two possibilites to get this type of issue.
1.There may be a problem in your Sim card so try another one.
2.Your iphone is locked by some network.
If your problem persists after trying another sim card means definitely your iphone is locked by some network.So try to unlock your iphone.For unlocking you can approach your service provider or else try to buy an unlocking service from any one of the online unlocking service provider like
OnlineGSMUnlock.com

If you have problem in accessing with any specific SIM card in your iPhone, You can make a complaint to your network provider and get a new one.
If you are not able to access any SIM card in your iPhone, Take your iPhone to a local mobile store.
If you are not able to access any SIM card other than a specific SIM card in your iPhone, then your iPhone must be network restricted. You need to unlock it.
The safest and easiest way to unlock an iPhone is to unlock through remote unlocking method. You can get the remote unlocking for an iPhone from www.wickedunlock.com/apple/rs11wp8/ at affordable cost. This method of unlocking doesn't require a Jailbreaking too.
Here are the steps to unlock an iPhone,
1. Wait for us to send you an email saying your phone has been activated or remotely unlocked.
2. Install the latest version of iTunes.
3. Make sure your Apple iPhone phone software is updated to the latest version using the iTunes software.
4. Connect your Apple iPhone to iTunes with a NOT ACCEPTED SIM card.
5. Wait until iTunes detects your Apple iPhone.
6. Disconnect your Apple iPhone and reconnect it after 10 seconds.
7. Your Apple iPhone is now unlocked.

No Sim Card Installed Insert a valid Sim with no pin lock

this is what you do

1. get a unlock card Click Here
2. get a Verizon Sim card click here
3. Switch off 3G network: Setting---General---Network---Enable 3G---Off
4. Turn off the iPhone 3G, take out the SIM tray, place the Unlock Card and the SIM card on the SIM tray, put back the SIM tray into the iPhone
5. Turn on the iPhone
   There is NO NEED TO CUT YOUR SIM!
6. Just Plug & Play!

the new sim card is connected with having an iphone account. when you say it is officially unlocked.
does this mean that AT&T unlocked your phone?
what i think your saying is that if you have 2 sim cards, one that is in use and the other is a spare you cannot use both. at the same time.
the sims are standalone, to use a spare sim it has to be activated by the carrier, thus disabling your original sim.
when you change sims you will need to reboot the phone that will not change.

this is what you do

1. get a unlock card Click Here
2. get a Verizon Sim card click here
3. Switch off 3G network: Setting---General---Network---Enable 3G---Off
4. Turn off the iPhone 3G, take out the SIM tray, place the Unlock Card and the SIM card on the SIM tray, put back the SIM tray into the iPhone
5. Turn on the iPhone
   There is NO NEED TO CUT YOUR SIM!
   
   
6. Just Plug & Play!