Q: What is cellular data on iphone 3gs?

Yes, you can surf the net, if you have wifi and have cellular data off.

This is usually done, when your going on a trip out of the country and don't want an expensive phone bill.

The "3G" network (UMTS) carries both voice and data.  If you have cell data disabled, and use WiFi only, you don't get charged for data, even when using 3G for voice calls and SMS.

ok so i want to turn off the 3g internet only so i can still recieve/send texts and call and still use wifi, but if have no wifi connection i dont want my phone to use the 3g internet. to do this i turn off cellular data and keep 3g on?

If you disable BOTH WiFi and cellular data, you have NO internet connection at all.  You can still make calls and SMS text, but that's all.  If no WiFi is available, your only choice is to enable cellular data if you want any internet connection.

i have the same problem ..... even i opened my cellular data .. even i have load for internet connection .... i cant use it ...