No, there is no way to flash T-Mobile branding onto the device. To get the Wi-Fi icon lit up, try sending the service books. Log in at my.t-mobile.com and (at least for the moment) hover over Connect & Share then click toward the right where it says Configure E-mail. There's a link on the left for Service Books that will let you send them to your phone. I don't know if the voice command language is changeable, my Flip has only English.
It is possible to get UMA working, but it is not for the faint of heart or clumsy of thumbs. You'll need to install the T-Mobile UMA profile using the engineering screen on your BB. Which means you'll need to gain access to the engineering screen on your BB. These screens can brick your phone, so proceed with caution and don't change any unrelated settings.
Do a web search for the free "BBEscreen" app, or buy the paid version from the CrackBerry App Store. (There is also an escreen python script for the geeks among us.) This app will generate a timed access code to get you into the engineering screens for between 1 and 30 days.
The below web link has instructions for installing the T-Mobile UMA certificate and configuring the UMA settings using the engineering screens on your phone. Disregard steps 2-7 and instead use the BBEscreen app or python script to generate the e-screen access code.
Use any UMA enabled BlackBerry on T-Mobile | BlackBerryRocks.com