Ever since I updated my iPhone 4 to iOS6, I'm not able to connect to the internet except when I have a WiFi signal to connect to. Any suggestions about the cause or solution?
There are multiple things to check on (in the order you should try them):
Although the latter isn't the ideal solution, it might solve your issue. But only try this in worst case scenario (since it's pretty radically).
Anyhow, if neither of above options solved your issue, you're not alone. I recommend you pay a visit to your Apple Store.