Q.1 How can the system locate a user?
You’ve identity (of your mobile) stored in a System (Similar to a database) called HLR.
Q.2 Why don’t all phones ring at the same time?
Your question is too vague. Phones can ring at the same time.
Q.3 What happens if two users talk simultaneously?
Again, it is a vague question. Still one radio channel (ARFCN) can accomodate 8 users at the same time. So, just 2 users talking at the same time is not a problem.
Q.4 How secure is the mobile phone system?
It is upto the operator to tune their system security. We have A5 & A3 algorithm are available for security over radio interface.
Q.5 What are the key components of the mobile phone network?
BTS -> BSC -> MSC -> GMSC -> HLR