It doesn't matter where you bought your phone or what sim card you are using or what location you are using it in. What does matter is the CSC code, (Consumer Software Customisation code). To find your CSC code... go to the dial pad and type in...
*#1234#
You will then get a screen showing, "Version", with 3 lines of information.
The last line, CSC, is specific to geographical region and carriers. It contains the software packages specific to that region, languages, carrier branding. if any, and also APN settings for data connection, MMS etc for your service provider.
Typically, CPW in the past, although having their own CSC code, have relied on and linked their firmware to the UK, unbranded, firmware release.