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I activated my internet browsing which turned on the 3G function.
However I can't turn it off and it keeps dropping my credit balance down.
OK I can see no one is going to reply to this post. Thanks a bunch guys!
My suggestion is go to the android market and download "2G - 3G OnOff" by Curve Fish thats just a quick link to
Settings -> Wireless Controls -> Mobile Networks
now under Mobile Networks, uncheck MMS & Data
a message will say if you're sure you want to disable MMS and Internet, click Ok
I take it your an American?
I'm in the UK and there is no MMS and Data on Mobile Networks.
Will the widget by Curve Fish actually work with my phone?
Go to setting -> wireless controls -> mobile networks -> network mode -> select GMS only... but I don't think it will turn off the data transmission
you should go to setting -> wirless controls -> mobile network -> trun off the MMS and data option.... that will shut off the data transmisson and message (text and pix)
hope this help!!!
Go to android market and download Quick Settings, that will do the trick aswell.
cch0104 and uniwooly are both correct...
Settings -> Wireless Controls -> Mobile Networks
I'm in UK too, and "mms and data" should be the first thing on the menu... just check or uncheck the box

It does turn off picture messaging (MMS) but text messages are not affected by removing the tick in the 'MMS and data' box.
thanks for correction about the text message~~~~ 
Certainly worth knowing, I use text messages all the time, but I never have my data and MMS thing enabled, unless I get a text saying that I have a picture message and I can't see it otherwise... 