How Does a Cell Phone Get Call Notifications, SIM Key Role, and Signal Filtering Circuits?

Hi, I want to ask how a specific cell phone get notified that someone are trying to call you right now ? Does the SIM inside the cell phone has a unique key that is used to decrypt an encrypted signal coming from the tower ?

Another thing, when initiating a voice connection over cell phone network ... now the tower broadcast the signal in all directions in a range of few miles and any antenna within this range will receive the signal so the signal has to be encrypted using again the SIM unique key, right ? And the last question is that the antenna of a cell phone will also receive signals related to other voice calls or even other towers, now these additional signals represent interference to our voice calls, and the solution is using filtration to focus on a specific range of the spectrum and remove the others,my question is what's the electrical circuits used in today's cell phones to do this filtration ?

My regards,

Hi. By definition, SIM or Subscriber Identity Module is an integrated circuit that stores necessary information about the subscriber.

To answer your questions, I find this site useful.

http://www.ehow.com/how-does_5369478_sim-cards-work.html

Regarding your question about filter circuits, did you mean the RF and microwave filters? These filter circuits are designed for GHz and MHz frequency ranges.

Thanks Nikki Martinez ... I found a very useful link too
http://electronics.howstuffworks.com/cell-phone.htm

Lots of details in this link .