help in interfacing using microcontroller

hi,
im doing a project based on multipurpose security system using GSM using PIR (passive infra red) sensors to detect human motion at d entrance of bank vaults etc n also an alphanumeric lcd display will be placed at the entrance so any person entering has to enter their secret password and then an sms will be sent to the administrator's mobile phone stating the details of the person who is entering and immediately a real time clock will start only for a certain amount of time and once the time limit is crossed a buzzer will ring and another message will be sent to the admonistrator stating that the customer has exceeded his time limit. we will be using an 8051 microcontroller connected with a GSM module and a DTMF encoder and decoder.
my question is how can we incorporate more things into this project like cann we interface more sensors or sumting???? plz reply soon!

you need these port pins
LCD 4 + 2 = 6 pins
PIR = 1
GSM = 3 (tx rx and GND (Serial UART))
Buzzer = 1

why do you need decoder for this.... without this also you can do.......

---------- Post added at 12:07 ---------- Previous post was at 12:06 ----------

phone number can be stored in flash of controller, so no need of external eeprom... out of 32 pins you are using 11 pins only... what is the issue.....