We all use the mobile phone so much it's an integral part of our communication.We all know that any mobile phone cannot function without a SIM.How to get it is widely known;you can get it through any telecom retailer,showroom even the paan -wala's have the stock now....You just have to give a bunch of documents and photographs and its done..But when you have a SIM,there's more to just a number....Let's know it better. A SIM is the shortform for Subscriber Identity Module. The name itself explains that this chip is actually a module that contains your information.What would that information be? The SIM is designed with unique codes that is used for (a) Identifying you. (b)Stores information about your number (c)giving your services of your choice available with the operator like SMS, Roaming,STD etc. Roaming and STD facilities are assigned to your number only after your verification is done.In India these facilities are freely assigned but in countries like Europe and USA,these services are only assigned on request with some operators. When you purchase a number, your 10 digit mobile number is mapped to a 19 digit number.You can find this printed at the back of the SIM.This is called IMSI number. IMSI? IMSI -International Mobile Subscriber Identity or generally known as service-subscriber key. This is again a unique code that helps in tracing your number and ciphering your information. Well,you might be thinking,if this is a key then there must be a lock as well. Yes,there is. It is called The  PUK. You are aware that you can put in a PIN to protect your mobile information. PIN ( Personal Identification Number) can be set by the mobile company and reset by the customer himself/herself. Many a times there is a wrong PIN set and after a  few attempts your number gets locked. Well,this is a cautionary step taken by service providers to ensure the mobile is with you.Incase you loose it,any other person cannot access your personal information without the PUK. Coming to PUK- Its called the PIN Unlocking Key.This number is only with the operator and you can get your  PUK from the operator when you lock your device accidentally. Your SIM also has a memory.It comes in 32k or 64k cards so that you can store around 250 contacts in the SIM and if you fancy you can also store a few messages as well.Its called the SIM Card Memory.If you loose your SIM and don't have a backup to this memory in your device,you cannot get the information back. What does this SIM do? Well basically; when you dial a number and try to connect,your call gets routed (thats another interesting topic,I might discuss later). For now,your call gets connected to the nearest tower where the server there recognizes your IMSI number and allows you to make the call within the network. Thats why when you are in Roaming,you have to select a network either Automatically or manually inorder to make calls.Once your IMSI number gets verified ,your call details are logged.And then comes the bill that we all dread! So basically your SIM,a chip,allows to make calls,has all your information,has a security lock and what else? It also helps you enjoy VAS (Value Added Services).Remember I mentioned that STD and Roaming get mapped and assigned,well so does all the Value added services like your Dialer Tune (Hello Tunes),Joke Packs and so on and so forth . When you walk-in a showroom and just pick up any number and take the SIM,you should be aware that all that information you provide goes into this little chip.Every detail is mapped to the payments you made or the one you didn't make,you address,your alternate numbers,your additional information.Imagine the magnitude. This chip if not guarded may get lost,you contacts are gone.If you loose your mobile and it does not have a PIN,any any fraudulent call is made....the calls will be traced to your number. I believe,its but obvious and a must to say here that genuineness matters.Everything is authenticated,so if you are careless enough to give in any personal information to anyone without thinking- you should be careful because it can be misused.This is not just a technical saga of what we have.Be sure that you are cautious about the device you own and the information you share.Incase there is a misuse-the loss to bear is huge! We say Information is wealth,well it is! And safeguarding it is only in our hands.