Does anyone know what the Cell Broadcast code is?
Cell Broadcast is almost completely redundant, after the rise of sms and internet
In the past, in theory people might subscribe to information channels about news or sport, or whatever locally based messages might be available.
The area code is the only thing left from O2. It shows the number prefixes of the nearest 3 or 4 landline exchanges, not just one. It would have been a lot more relevant when GSM started and some tariffs had cheaper calls when you were in your home area, like 25p a minute when local and 50p elsewhere. Nowadays, it's a bit of a novelty for a while, but maybe people eventually turn it off.
To use it, there will be something somewhere in the phone menu under messaging, and you subscribe to the channel number. Even then, it may be that you have to go to read the messages rather than see the info on the screen all the time, or perhaps depending on the phone some standby plug-in would be needed to make it appear there (this last bit is a guess)