Great question! Here are steps for both software versions for your Amaze. If you haven't updated yet I highly recommend it!
ICS Android 4.0:
These steps do require a computer and you will see 2 different drives appear when you plug in the USB cable. One labeled HTC is your phones storage and the other will be your SD card.
You can also download a file manager from Google Play to manage everything directly from your Amaze.
Hope this helps!
I agree with ed. You should be able to move your music from one drive to the other. As long as their is not a copy protection issue. I can't really speak for music...because I do not use my phone for that, I have an iPod Touch for that. But anything else I do works in that manner. Good luck. If this solve you problem...be sure to let the community know so other can use this to help themselves.
This time agree with clearkilling.
1. Make sure sd card is in phone. If it is not in the phone...put it in there.
2. Plug your phone's usb cable into computer
3. Plug phone into usb cable.
4. Select "Disk Drive" on your phone.
6. 2- Windows will open on your desktop. One of the is your phone's internal storage. The other is sd card storage.
7. Open both storage devices and find the files you want, select all, click and drag them from phone storage to sd storage.
That's what I do to move stuff like that.
Sorry you are still having trouble with transferring your music. You are going to have to improvise a bit. The steps are for a computer but instead of moving the music from a drive on the computer to the SD card you will be moving them from one removable drive to the other. Like I said above the phone storage will show as HTC and the SD card will show as a removable disk/storage drive. This is the T-Mobile supported way of moving files from the phone storage to an SD card or computer.
Or as I also stated you can download a file manager from Google Play. This would not be supported by T-Mobile as it is a third party application but is still a viable option for you.