I am using opera mini on my Blackberry using WiFi and never had problems connecting to Internet. But recently when I activated BIS ( Blackberry Internet Services ), Opera Mini refused to connect with an error
Unable to connect. Please review your connection settings.
To solve this you need to go Looking into settings > advance > protocol and switch from socket to http.
Done this, you will be able to connect to internet. In case u use wifi, you should make a switch again. I think opera should have an option for automatic switching and use wifi when available.