Iphone sim lock? - Nokia 2600

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

What's your exact iphone model no?
Before activate your iphone with your amaysim,Make sure your iphone is free from any network lock.Because there may be a chance to get sim error while insert your sim on your network locked phone.If it's locked by particular network,you will need to unlock your iphone.For unlocking visit ProUnlocking.com Here you can unlock your iphone 3 by Remote unlocking method without jailbreaking.I hope it will be very useful to you.

Hi if your iphone 4s is not accepting your sim card whether it is displaying messages like sim invalid ,sim lock and so on once you insert your sim in it then it mean your iphone 4s is locked to some other network provider due to this it wont accept your sim until you unlock it .You can easily unlock your iphone 4s using sites like WickedUnlock.com here they are rendering remote unlocking service to unlock all model iphone from network lock ...You first check that whether the service is available for your country and network provider .If yes then pay for it and unlock your iphone 4s then freely use it with any GSM sim .

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.

Is the iPhone locked to a particular network carrier? Maybe the SIM card you are using is for another carrier.

e.g. iPhone locked to O2 (Verizon, AT&T, Vodaphone) but SIM is for T-Mobile or 3.

Your iPhone says "Invalid Sim" means that your phone is locked to particular Network.To solve this problem, you need to get your iPhone unlocked.You can get your iPhone unlocked from Network lock using Remote unlocking method.Which is the safe and secure method to unlock iPhone.You can get this service from Unlock-Zone.com here you need to specify your country,Network name to which it is locked,IMEI number of your iPhone.And you can get free unlocking free unlocking instructions from MobileUnlockGuide.com using this you can unlock your iphone from Network lock easily.

Is the sim card installed belongs to the wireless company that the iPhone is locked to, or is the iPhone sim free?
If not, try contacting the company that the iPhone is locked to to try to unlock the iPhone to sim free, or get a sim that belongs to the company.

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

You can either return to the carrier and request a SIM unlock. However, in most cases you will need a new SIM card to resolve the problem.

I assume that your iphone is not locked to any cell phone company ...

Insert your SIM in your old phone/another phone and remove the SIM pin lock/password, then try this unprotected SIM again in your iphone. Once it is accepted in the iphone, put the SIM lock/password back using the iphone.
Hope it helps.