Unless the tablet offers a USB port (doubtful) and supporting software, it's pretty unlikely that Apple might support using solutions like the new United States-based DataJack service, which provides unlimited 3G data for 40 bucks a month. The MiFi router solution would work to provide 3G connectivity over Wi-Fi, as it currently does with iPod touches and laptops. MiFi service isn't particularly cheap, involves carrying around an extra hardware device, and is best suited to the hardened road warrior who doesn't mind paying $60/month for the convenience.
I've heard iPhone tethering floated around as a possible solution to augment built-in Wi-Fi, as well. Users carrying both an iPhone and a tablet could use the 3G connectivity of the former to power the net services of the latter, when out of W-iFi range. It's a nice thought -- but in the United States, would AT&T really welcome a further strain on its 3G network without additional revenue? Of course, if Apple did manage to swing a deal (say $10/month extra for tablet tethering only), it might explain why AT&T missed its "tethering this year (2009)" deadline.
Regardless of how the tablet might hook up to the net, it's likely to be just as bandwidth-hungry as the iPod touch and the iPhone, if not more so. With more pixels to fill, any streaming video content will demand more data to display. Add in an e-book store for reading on the go, as well as movie rentals and the App Store, and tablets will continue to expand the way Apple mobile devices consume purchasable media. And that's not even considering the everpresent rumors about front-mounted cameras and possible video conferencing.
Apple's iPhone and iPod touch business model has put a lot of emphasis on end-user shopping. Purchasing on the go has go to be a big part of Apple's tablet business plan moving forward. Consider Amazon's Whispernet service. It allows end-users to purchase media on the Kindle device. Powered by Sprint EVDO service in the US and by AT&T internationally, Whispernet downloads content from Amazon regardless of where users are. You can buy books while commuting, while at home, while at work, or at the park for lunch. Ubiquitous purchases form the backbone of Amazon's Kindle success story.
There are constraints to ubiquitous data network access, however. Whispernet limits Internet access to purchasing and downloading Kindle titles. Users cannot easily use this service to generally access the Internet (although the Kindle does have a basic browser). Amazon is providing a convenience that benefits both itself and customers, but these conveniences do not extend that to the kinds of day-to-day tasks like checking e-mail and full-featured web browsing that are so common on the iPhone and iPod touch. Users who want to read particular websites are allowed to subscribe to them, usually for a small monthly fee.
Even on the Kindle, Amazon's approach works, in our opinion, mostly because E-books are tiny. Shopping and product fulfillment place little demand on providers. Could Apple offer a similar shopping service for its tablet? Hard to say, because audio (not to even mention video!) would require a much higher load on services.
It's imaginable that Apple might launch a text-only "purchase wherever you are" system to take on the Kindle head-on, and expand that to audio and video as 4G (and later) infrastructure grows. It's also imaginable that Apple has evaluated the trade-offs between sales, commissions, contract terms, and rights owners and decided this is not a feasible path due to their relatively tiny margins. And, it's extremely imaginable that Apple has evaluated the strength of the jailbreak community, which opens up the iPhone's underlying Unix operating system for general computing use, and decided that a Whispernet-like approach would be too easy to exploit.
In the end, where "mobile" and "media" meet, which is where I envision the Apple tablet playing to its strengths, connectivity is going to have to play a huge role. Buying on the go, accessing already purchased data on the go, and general net access will be the questions raised and the solutions needed. I'm looking forward to seeing how Apple has realized tablet connectivity and where it will take us as media consumers.