How to disable 2G and 3G connection on Samsung Galaxy S?

[Elle]

I have wifi at home, and that's the only internet connection I want on my phone.
I'm on pre-paid and my phone is connecting to 2g or 3g without me knowing. It's charging me at 12:00AM almost every day and devouring my credit.
I have already made sure my apps don't have "sync automatically" ticked, so they shouldn't be syncing, and the auto-syncing option for my social media is also unticked. Help!

[Xavier]

it should be in the settings under phone and just turn on airplane mode. it turns off all wireless communications in one button but you can just go to wifi and turn it back on to use that.

[Stevie]

If you hold the power button it comes up with several options, just select turn off data network mode and it will not connect to the internet. Just to let you know 3G and 2G is also used to send and receive texts, using turn off data connection will not prevent you from recieving texts.