Fixing iPhone - Could not activate cellular data network. You are not subscribed to a cellular data service.

I bought a new iPhone 3G last week, and I was very satisfied with the phone.

But I had some problems when trying to access internet through my 3G sim card (with WLAN disabled). I kept getting the message:

Could not activate cellular data network. You are not subscribed to a cellular data service.

After a couple of tries I found the solution as follows:

1. Click on Settings --> General --> Network --> Cellular Data Network.

2. Under APN type in your provider, in my case I typed in:

internet.telenor.se

3. After doing this I was able to access Internet without any error messages.