At 8am this morning Plastic Logic announced that it will be partnering with AT&T to provide wireless 3G connectivity on its eReader device, expected out in Q1 2010. This announcement follows the news of Barnes & Noble's partnership with the device-maker.

No doubt, having big brands like B&N and AT&T on its partnership roster helps Plastic Logic establish credibility in a market where it is an unknown, competing against mammoths like Amazon and Sony. And the announcements help inspire confidence that the device will actually get to market–an assumption that can't be taken for granted given the pre-launch financial failure of other eReader competitors like Polymer Vision.

We think cellular connectivity–not just wifi, which isn't available everywhere–is table-stakes for Plastic Logic (and Barnes & Noble) to have any hope of competing with Amazon. Consumers value the seamless connectivity of the Kindle's Whispernet service, which lets them download a book in 60 seconds using Sprint's network. Especially since Plastic Logic will be focused on newspapers (USA Today and The Financial Times are also partners), having the device be able to connect and refresh content anytime, anywhere, will be crucial for its success.

What we still don't know: the financial terms of the deal. Will it be a wholesale model with a per-user monthly fee, like Sprint's arrangement with Amazon? Or will consumers be charged directly for a monthly data plan, like AT&T does for Apple iPhones? Will AT&T get a cut of every transaction, or just a per-user fee?

What we do know is that the big remaining competitor in the US mobile market, Verizon/Vodafone, won't be able to sit this one out. Our prediction: We'll see them partner up with Sony, First Paper, or both, before the end of the year.