But i believe there is no data plan for prepaid right? since CL state that he "topup"

btw CL, the only solution is you have to use data plan, if maxis then you cna buy data bundle in garage sales( it so hard to find it these day) and if postpaid can apply data plan.

but if you update to iOS4 you can disable data service on your iphone but when ever someone want to send MMS to you then you must open the data service in you iphone.

but truly speaking its better to have data bundle especially in iphone because we can use it to its limit