the technique of entering gibberish on the APN column might not work on the maxis network network anymore (since they are now the official malaysian carrier).
If u wanna change the APN, just swap it with another "non-official" service provider sim card (can do it while the phone is on) then go edit the APN setting to anything u want, and then swap back to "official" carrier sim card.

Another new method is simply to change the .ipcc file via iTunes (Carrier update): http://forum.lowyat.net/topic/752226

Post reference: http://forum.lowyat.net/topic/959711/+1840

(credit to nokia2003 and psyeo)

The answer is in here bro...
---> http://forum.lowyat.net/topic/868281

its in the section B no 1

Phone Credit Flying Out The Window? Turn 'OFF' EDGE
( Its on post #4 ).

cheers.
taka.

its ok, nothing to be sorry about...^^

so, does anyone know other ways to disable the EDGE/GPRS other than the APN technique?
doesn't want to jailbreak my iphone if possible......

I face the same problem with you when i tried the same method as posted...however there is a trick..here is how i resolve it...

1) start up your iphone with non maxis SIM (digi, umobile, celcom)

2) once started, you should be able to go to the (General -> Network -> Celular Data Network). There is where u can key in 'disable' to disable the 3G/EDGE. But wait, don't key in yet with ur non-maxis card still inside.

3) Back to the page where u can still see Celular Data Network, right now, eject your SIM card and swap it with your Maxis SIM now. Once swap it in back, only tap the Celular Data Network.

4) If you previously have updated the Carrier Settings, now you will still be able to put in disable or some other words other than unet, maxis or wap. Once everything is key in, go back to your home screen. Time for testing. Test the Weather channel, Safari etc.. You will received the error, you are not subscribe to the celular data network service etc....