A cell phone is a device that accesses a large RF wireless network and giving the end user the ability to make and receive phone calls, send and receive email, text messages, data, video.
How do cellular phones work?
When it comes to cell phone basics, essentially every phone has a serial number, identification number of some sort that is unique amongst every other device that's on the network. With that being said, every time you turn on your cell phone, that number transcribes into your telephone number, into you as a person, your name, your personal information, all that. Once your cell phone is on the network and registered, when it says "Hi, I'm here. I'm so-and-so's cell phone", it's basically saying to the network "I'm available". Then, when a call is placed and when you make a phone call, it basically does what's called pinging a server. Here, it checks to see if the other end is open to receive a connection. When it does this and says "Ok, there is someone here and we'll take a call. What are you going to do?" This is when your phone rings and you say answer or ignore. If you click answer, it sends a message back to the tower saying "I've accepted the call" and then starts transmitting the voice data that goes into the microphone. Then, it gets transferred into smaller pieces of information that can be sent wirelessly over the network to the towers and on to the other end.
Why does my cell phone reception vary depending on the area I'm in?
With regards to the basics of cell phones, cell phone reception comes from a large tower that comes out of the ground which transmits a signal. The tower transmits a beacon and that beacon transmits it via a wave. That wave is an actual radio frequency that sends a signal from the tower to the handheld cell phone device. When that wave is in any way disrupted, you see deterioration in the signal strength and therefore have low cell phone reception.
What is a "Subscriber Identity Module" (SIM) card?
With cell phones, SIM actually stands for Subscriber Identity Module. Essentially, a SIM is like an ID card for your telephone number, and that ID card is specific for the network. When you sign up with a new service on a GSM carrier, GSM carriers use SIM cards to define who people are. So, when you give me your name and I set up your account, the SIM card number that I put in there is your unique identification for the network. Once your cell phone's turned on, it actually takes that unique identification and sends it to the network so that the network knows who you are and where to route the phone calls to.
What is the difference between a "locked" and an "unlocked" cell phone?
With cell phone basics, the difference basically between an "unlocked" and "locked" cell phone is that a locked phone comes directly from the carrier. So, Carrier A has the phones that they test, set up and have already preconfigured to talk to their network and transmit data with and whatnot. Whereas an unlocked phone however, is directly from the manufacturer, it comes from Motorola and Nokia. The carriers don't ever touch them, because of that, they can use whatever SIM card they want inside, whereas a locked phone can only take Carrier A's SIM card, or, a Carrier B locked phone can only take a Carrier B SIM card. In contrast, an unlocked phone can take either/or SIM card.
What are "peak", "off-peak" and "mobile to mobile" minutes?
Peak minutes generally are minutes that are calculated between the hours of 7:00 AM and 8:59 PM. That's when the network sees the most usage. That's why the minute pools that you get, that you pay for per month, are taken out of that time, because it's the time that people most often use their phones. Off-peak, however, is a time when the network is idle or people are sleeping, or eating dinner. There's just not that much load in the network, so you can be free to use that as much as you want. Mobile to mobile, however, is basically giving the customer the ability to call another handset on the same carrier. So, if you're with carrier A and you have a telephone, and your friend is also with Carrier A, anytime you communicate between the two it's free, because there's no drain in the network; there are no outside transmissions going on. The way that call centres work is that when you make a phone call, the first network gets it, and when your network gets it, if it's a call within your network, then that call centre distributes it to the next person. Whereas, Carrier A gets the call, and it's to Carrier B, then it has to call Carrier B's server, and Carrier B has to find the user and then make the phone call. This makes an outside connection, therefore putting more drain on the network.