@sniper msia:
No, the voicemail has to be cancelled in order for your ringtone duration to be increased.
@jdreamer:
If you'd read more carefully, you'd notice that I didn't state that there were any disadvantages.

To increase your ringtone duration, two services provided by Maxis will have to be cancelled. They are:
1) Voicemail
2) Missed call notification
You can't increase the ringtone duration by yourself. You'd need to contact the Maxis Customer Support to do some changes in your account on their end.
But on
your side, you'd need to do some manual configuration as well. That's when you type the command *147*0# and press the Call button on your phone.
But you should only do so
after you've contacted the Maxis Customer Support, and only if you plan to increase your ringtone duration.