The myTouch has been made by HTC and LG, but I believe they are both moving on from making phones under other companies' brands. Plus, I'm sure T-mobile wants to pay at little as possible for it. Here comes Huawei who is willing to do that for them and start getting some name recognition in US, just the way HTC started, too.
I've long believed that Huawei is almost following HTC's path, by wanting to enter the smartphone industry first by making devices for other companies as an OEM, and then by slowly promoting phones under their own brand. It's a good strategy for such OEM's, but it takes years to get to the point where they can be seen as a top brand.
This is why Huawei has promised that this year they will also work on heavily promoting their Huawei brand and by making some of the highest quality and most powerful phones and tablets. If they keep this up like with their Ascend devices, I'm sure they will be successful, and they soon might even surpass LG and other more known companies in the smartphone industry.
But until they get there, they will still try to capture as much market share as possible as an OEM, and get their name subtly recognized in western markets, like with this new T-mobile myTouch phone that is made by them.