SIM Card Unlocking Codes and Associated Restrictions

what is a sim card? why is my sim locked? how do I unblock my sim?

what is a sim card? why is my sim locked? how do I unblock my sim?

First of All ….. What is a SIM Card?

The Subscriber Identity Module or SIM is a removable chip that is inserted into a GSM mobile phone and is usually concealed behind the battery. It is a small piece of  plastic with a printed circuit board on it that has been programmed by the manufacturer on behalf of the Network Carrier who issued you the mobile phone. A SIM card is also like a small hard-drive.

The SIM usually contains data that defines:

  • Personal identity information like phone number, phone book, text messages and data.
  • The MCC / mobile country code
  • MNC / mobile network code
  • MSIN / mobile station identification number
  • Possibly ID’s / voice group call service
sim card is issued by a cell phone's wireless network provider
SIM Card
What are the advantages of a SIM card?
  • One of the biggest advantages of using a SIM cards is that you are not cell phone restricted. You can place the SIM card into another phone and it will work with your same number and network.
  • The advantage of having a cell phone that accepts different SIM cards is that you are not SIM card restricted. But first you have to get the mobile phone unlocked. Once unlocked a mobile phone will accept SIM cards from other networks and will work on the frequency and bands of different carriers.
  • An unlocked phone can mean major savings when abroad; by purchasing a local pay as you go SIM card you can save on roaming charges.
  • You can upgrade to a new phone by just swapping the SIM card.
What is  a Locked SIM Card Code?

Locking of a SIM card is a feature built into most GSM Mobile Phones by the manufacturer with the specific intent of restricting use of the phone to the network provider and / or country which issued the handset.

The locking feature is referred to as a SIM lock, network lock, simlock or subsidy lock; the latter reflecting that most post pay cellular phones are discounted as an inducement to sign the service contract. They are entitled to recoup the subsidy over the life of the contract.

Invalid SIM Card or SIM Card Error Message

If you are getting an Invalid SIM Card or a SIM Card Error message, then it indicates that your mobile device remains tied to the issuing Network Carrier and you have inserted an invalid SIM into your handset. If your phone is still locked it will not recognise a SIM card from a different network provider. You will need to get an unlock code to have the SIM card network restriction lifted.

Unlocking a SIM Card or Unblocking a SIM Card

Unlocking a SIM card is not to be confused with unlocking a mobile phone. A SIM card lock or block is different and happen when the security PIN number is entered incorrectly. If a SIM card get locked, the phone will usually display a message asking you to enter the PUK code. The PUK number when entered will unblock the SIM lock. Obtaining the phones PUK or PUC code is done by contacting the SIM cards wireless network provider (ie. Orange, O2, Vodafone, Movistar, etc.).

Where do I get an unlock code to unblock the SIM lock restriction

A mobile phone can be unlocked by entering a code provided by  Then just follow the easy how to enter an unlock code instructions and it will unblock the SIM restriction and your phone will work with SIM cards from other networks. Recognised unlocking services such as offer a guarantee, value for money and a step by step guide to protect you from error.

micro sim card for smartphones and tablet computers
What is a Micro-SIM?

A Micro-SIM is an even smaller SIM card. They were created for smaller devices but are compatible with regular SIM cards. The contact area of the chip on a Micro-SIM is the same. The length and width have been reduced to 15mm x 12mm. The Micro-SIM are very popular on newer smartphones such as the iPhone 4 and on 3G tablet computers like the iPad.

What is a Dual SIM Card?

Some mobile phones are Tri-band. This means that they are capable of working on different networks and on different frequencies. This is especially useful if you are planning to travel to and use your mobile phone in another country. The countries in which the phone will accept service in will depends on which three frequency bands are on the phone.

Some phones have slots for two SIM cards. These are know as Dual SIM card phones and can give a cell phone user an additional phone number with which to work. You just switch back an forth to determine which SIM card you want service on. If you use a different network, the phone must be unlocked or a SIM card from a different service provider will not not work on a DUAL SIM phone.

Why don’t CDMA network phones use a SIM card?

CDMA network providers identify mobile phones on their network with the use of the handsets ESN (Electronic Serial Number). A CDMA carrier does not support the use of SIM cards. SIM cards are used by GSM (Global System for Mobile Communication) wireless networks. In the United States Verizon and Sprint are CDMA carriers while AT&T and T-Mobile are GSM networks.

What is a SIM card reader?

A SIM card reader is a simple machines with a digital display screen. It allows you to insert a SIM card to read and edit the information stored on the chip. Information such as contacts, phone numbers, data, and text messages. They are used to back up data and protect against loss or damage of a cell phone SIM card.


The SIM card is an essential device for modern telecommunications. The ability to transpose our phone number and device data by simply transferring it onto another mobile handset makes it versatile and practical. It does not leave you SIM card restricted or cell phone restricted because on an unlocked mobile phone you have the choice of what SIM card you want to use. Remember if you are getting an Invalid SIM Card or SIM Card Error message then you need to get the unlock code for your cellphone and have it unlocked.

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