how do i see or listen to my voicemail online

Mine also does not work this way, it must be because it’s part of a corporate account.

However I had my other mobile phone with me and I was able to install the DIGITS app on it (an official TMobile) app and see my texts and voicemail on my other phone, and to make/receive calls as if I had my TMobile phone with me! You can also access DIGITS on a PC.