Why Nokia went EE/Phones 4U Exclusive in the UK.
Firstly, Phones 4 U sold 52% of all Windows Phone's during 2011. Whilst the number of total sales was quite small, one retailer sold way more than carriers directly, their own high-street store's and other large retailers like the Carphone Warehouse.
Whilst everytime I have visited Phones 4 U, I have always been disappointed( e.g purchase of HTC Mozart, HTC Titan, a Lumia 800 on contract and now a HTC 8S on contract), if this retailer is selling a large proportion of the devices, then it make sense to go with them, one might argue.
I also think the 920 went EE exclusive so it could rival the iPhone and Android offerings on the UK's first 4G network. This is more about prestige and rivalling the big boys on a new network, with a huge advertising budget that Nokia doesn't have to provide directly. EE is everywhere, they've around 750 retail stores, adverts everywhere and so more people will see "iPhone, Samsung Galaxy, Lumia 920...". I have also seen EE push the 920 a massive amount in my city - a lot of billboard space that EE is renting displays the Lumia 920, rather than the iPhone or Galaxy S3.
In this instance, Nokia is getting a lot of advertisement and floor space, with a retailer who seemingly has pushed Windows Phone more than anyone else has managed to AND with a premium network. Perhaps to them the goal with the 920 wasn't crazy sales in the UK, but steady sales with brand building. You might also notice that the Lumia 920 is one of the cheapest handsets on EE's 4G network - only the Huawei Ascend P1 is cheaper.