OK, I'm making myself a hostage to fortune here, but my expectation is that the Apple iPad should be very low on the list of operators' worries when considering mobile broadband traffic patterns.
There's been a lot of speculation that it could cause additional problems above and beyond the iPhone and 3G dongle-equipped PCs, but I'm really unconvinced it's worth other than some cursory monitoring.
Firstly, even the optimists (I'm not one of them) expect the iPad to sell in far smaller numbers than the iPhone.
Secondly, not all of them (or even most of them) are likely to come with 3G modems. They're optional and not even on sale yet.
Thirdly, they are unlikely to be used for many of the "quick hit" on-the-go access to maps, email, Facebook and so forth that are characteristic of iPhones.
Fourth, they are being sold with the benefit of hindsight - and at least nascent offload / traffic management strategies. It wouldn't surprise me if operators adopt some very specific iPad policy and enforcement techniques.
Fifth, a proportion are likely to be used almost exclusively as "stay at home" tablet devices, plus the occasional trip out of WiFi range.
Sixth, most iPad owners are likely to have an iPhone, which will probably be used for applications that need to be "always on" or most frequently-checked and generate much
of the signalling load. For networks like AT&T's it has been the iPhone's constant setting-up and tearing-down of data connections that has been at least as much a problem as the sheer bulk of data downloaded.
Seventh, it lacks a camera, which means that uplink traffic may well be much lower.
The main variable is the potential of the device to be used to consume large amounts of video over the 3G connection. Frankly, in comparison, the downloads of newspapers or a few apps is trivial in data volume.