Dunno if anyone has tried this... Blackberry.alx
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I added the vodaphone and tmobile charm themes in. Next time you connect your device it says system core software needs to be updated. Allow it to update and it will install the new themes on your device.
Note: This is tested out with 4.0. Not sure on 3.7 software what will happen.
Now under themes I have T-Mobile and Vodafone along with the Default theme.