It seems that, pakistani hackers are just testing the security of there own country, as they are hacking there own country's domains. Earlier also, Pakistan International Airport callcenter site is hacked by the pakistani hacker.
Mobilink GSM is the largest telecommunication service provider in Pakistan. The company is Pakistan’s leading cellular operator with a subscriber base of 35 Million.
On the deface page hacker wrote a warning message to the site admin, as
Admin Secure Your Website Just a Warning I Don't Want To Mess With yOUR Data But Listen I Have All Your Data hahahaa thnxx:DBy the above message it is clear that, hack was to show the poor security of the Mobilink.
At the time of writing also, deface page was there and you can see it here.