well RIM works a lot but if you look closely, RIM's customers are the carriers and not you and me, who are the carriers' customers. So it makes sense that RIM releases exclusively to carriers.
From a carrier point of view, you would not have a customer call you and demand support for OS7.1 if you have not trained your hotline team to OS7.1 for example.
About the testing channel, you may find some interesting things at the BlackBerry Beta Zone. I have no information because French citizens are not allowed to enter the Beta Zone (yet).
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