Maybe O2 are going to try to upgrade it's network to EDGE? A bit pointless if you ask me, but if Apple really cannot yet produce a decent 3G version of the iPhone it might have to do. Using with iPhone with GPRS would be a joke (a sick one).
Perhaps they plan to include access to a network of wifi hotspots included in the data bundle - but that would only benefit some people in big cities. Does O2 have wifi hotspots?
No, but I guess they could do a deal to let iPhone customers use the BT wifi network. That would be good.