What is a PUK code and how do you get it ?

In explaining a PUK and its purpose, you first need to understand the SIM PIN.

A SIM can be “secured” using a PIN - the wisdom of doing so often being dictated by circumstance and need. Once a SIM PIN is enabled, the PIN must be correctly entered every time you power-on the device within which the SIM has been installed, otherwise there is no access to the Cellular network to which the SIM provides cellular service.

You have three opportunities to enter the correct SIM PIN. After three bad attempts, the SIM will lock.

A locked SIM requires a PUK (PIN Unlock Key) code to release the lock. The PUK code must be obtained from your Cellular Carrier, as this “key” is burned-in to the SIM when set-up by the Cellular Carrier. If your device prompts for a PUK code, having obtained the code from your Carrier, you typically have five opportunities to enter the correct PUK code; if the PUK code is not successfully entered on the fifth attempt, the SIM is permanently locked - after which the SIM must be replaced.

A PUK code is provided by the mobile network carrier and used as a “master key” to unlock a SIM PIN.

It can override a “personalized” SIM PIN which might have been forgotten.

It’s sometimes printed on the SIM “carrier card” (the credit-card sized chunk of plastic that DOESN’T go inside your phone)

Otherwise, you’ll have to obtain the PUK from your carrier.

Note that most carriers also set a default “personalized” PIN. If you obtain this default PIN, you can then personalize the PIN to a number you prefer.

More info on SIM PINs is available here:

https://support.apple.com/en-us/HT201529

You’re welcome. As you correctly observe, “experimenting” with SIM PIN and PUK is unwise.

SIM replacement is both inconvenient and potentially with financial cost.

Nice reply.

Never needed a PUK; have always “gotten in” w/ the carrier’s “default” PIN.

Since “experimentation” with in-service SIM PINs is just not a “good idea” …

… does using the PUK “wipe” any existing personalized PIN as well, allowing the owner to set his own 4-8 digit PIN?

The SIM PIN relates to the SIM itself - and is stored within the SIM, not the device. Remember, the SIM PIN protects the SIM (and its contents if used to store a phonebook) and nothing else.

The SIM PIN can be changed by the Subscriber whilst the SIM itself is unlocked; the PUK however is “burned-in” and cannot be changed.

The default PIN to which you refer is set by the carrier when initially setting-up the SIM for the subscriber. When (if) activating SIM-locking, or changing the SIM PIN, the initial “default” PIN must be supplied by the Subscriber. Once changed, the default PIN no longer exists - having been replaced by the PIN set by the Subscriber.

The PUK doesn’t wipe or reset anything. The PUK is only used to unlock a SIM that has been locked-out due to incorrect input of the current SIM PIN.

Yes, everything you said was spot-on and fully understood; clearly my question was not sufficiently clear.

Allow me another attempt:

If a user does NOT know the carrier-provisioned “default” SIM PIN … but DOES know the PUK (because it’s printed on the SIM carrier):

Can the PUK - by itself - be used as a means to “set” a new SIM PIN ? (i.e. without needing to know the pre-existing SIM PIN)

You were clear - as I hoped was my explanation.

As short and clear as I can make the answer:

No. The PUK is not used to reset a forgotten/unknown SIM PIN.

Thank you. 👍

That corrects my own mis-understanding.