Is it possible to use to arduino to read data ( line voltage, frequency etc) a UPS system is monitoring via serial communication?
Generally. Yes
The Arduino can read serial data. If you are using a board like the Uno etc, you will need to use SoftwareSerial because the hardware serial lines are used to communicate with the PC for debugging and programming.
It also depends on your UPS, I presume you know what data format it outputs ?
Also.. True RS232 uses voltages beyond 5V (the Arduino uses 5V RS232), so if the UPS uses normal RS232, you'll need to use a level converter IC e.g MAX232
Ok now lets say I'm able to continuously poll that data from the UPS system using that method, can I using the same arduino board to send that data to a web server and build a GUI using Matlab to display the data as well as send a sms when there is a change in state ( eg: the voltage being monitored, drops from its original value) ???
can I using the same arduino board to send that data to a web server
Yes. If you connect the appropriate external hardware, e.g. use external Wifi or Wired ethernet shield or equivalent
or use a YUN which has onboard Wifi
and build a GUI using Matlab to display the data
Not my field of expertise
as well as send a sms
Not sure if you want the board to send an SMS or the website.
Arduino can connect to GSM Shield to send SMS, but you'd need to get the GSM Shield and get a SIM that has credit to send SMS
If you know a good web sms gateway you could program the ethernet to send SMS via that gateway
But overall there are too many what-if's in your question, its too open ended.