05 Nov 2008 -
This Works only When there is server updation.Server updation normally takes place on certain days of a month from 1am-4am.You Can Call Freely during this time.
Just Check u r balance after 1am and when u get error msgs like Server Upgradation,U r free to call,make 1 call chk u balance and then continue.
This may work only few days a month but it works...depends on u r luck too...