On Monday, T-Mobile revealed it will have sole U.S. rights to sell one of Nokia’s new Windows Phone 8 devices: the Lumia 810, which appears to be a tweaked version of the new Lumia 820 being launched with AT&T. The device is optimized for T-Mobile’s unique – though rapidly evolving — 3G frequencies and appears to have a slightly different design and feature set from the 820. An official spec sheet hasn’t been released, but the most glaring difference between the two will likely be lack of LTE radios in the 810.

There’s a much bigger spec gap, however, between T-Mo’s 810 and the Lumia 920, Nokia’s new flagship WP8 phone, which will be exclusive to AT&T at launch. It’s not that the 810 is a bad device. It’s not that it isn’t pretty. But it’s a scaled-down handset compared to the 920, and it’s targeted at a more budget-minded smartphone user (T-Mo hasn’t released pricing details, but is emphasizing the 810’s “great value”). T-Mobile got the same treatment last year, when it landed the Lumia 710 only to see the much sleeker 900 go to AT&T.

It’s not that mid-range phones aren’t a good match for T-Mobile – its customer base often gravitates toward more inexpensive devices and data plans – but as my colleague Kevin Tofel pointed out last week, these kind of exclusive deals do no one any good (except for AT&T). Customers want to chose both their device and their operator. Meanwhile, Nokia is struggling to rebuild its brand in the US and shouldn’t be saving its latest and greatest for a single operator, no matter how big AT&T may be. Tofel points out:

“Nokia does benefit from having AT&T tout this as an exclusive flagship phone and from AT&T’s expected marketing to help sell the device, but I don’t think that will add more benefit than the value lost from selling the Lumia 920 on multiple carriers simultaneously. Look at Samsung’s recent Galaxy Note 2 estimates as an example: It expects 3x the number of sales as the first Galaxy Note in the short-term because of a widespread launch on multiple carriers. The device is expected to be on all four major U.S. carriers in the next several weeks and because of that, I wouldn’t be surprised to see Galaxy Note 2 sales in the U.S. rival those of the Lumia 920 by year-end.”

In the case of the mid-range device, the carrier may not benefit from exclusivity either. Here T-Mobile gets a device that’s purportedly exclusive but really has the same basic features and specs as the Lumia 820 AT&T sells next door. Its enthusiasm for promoting the 810 is further lessened by the fact that it isn’t even selling the most cutting-edge variant in the Lumia line. If T-Mobile carried both devices, there would be a good chance it sold more mid-range 810s than it did 920s, but at least it would have incentive to market its new Lumia portfolio as a whole, instead of settling for the devices that AT&T passes over.

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AT&T President Randall Stephenson hopefully has a few things up his sleeve for moving AT&T out of the dying landline business and increasingly toward the much more lucrative and future-proof mobile wireless market. Clearly, securing iPhone carrier exclusivity would be high among his goals then, since 4.3M iPhone subscribers joined up in the second half of 2008, nearly half of whom were new to AT&T.

Problem is, from where I’m standing, AT&T probably isn’t in a very good bargaining position at the moment. Sure, they’re building out their network as fast as they can to keep up with the additional strain put on their 3G network by iPhone demand, but what kind of carrot could they possibly wave in front of Apple to really convince them that selling their phone to more people on multiple networks isn’t the better deal?

The answer is money. They could offer Apple a revenue sharing model that is extremely generous, and subsidize upcoming handsets to the point where Apple could potentially offer the iPhone at a lower price point and expand their user-base even more. The key ingredient will be network buildout, though, since Apple is unlikely to stick around if AT&T can’t get its act together enough to even allow for more subscribers, regardless of how either company intends to attract them. That’s good news for current subscribers, because it means they should see significant improvements in service through at least 2011.

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