For the most part, Your phone number with area code will show on the bill as sender or receiver, regardless of where You are. As long as your ISP remains the same and/or use the same sim card. Now, other data configurations on your phone may or may not do what you are asking. For example if you use roaming, a 'mock location' setting or app, or if you reset your 'network operator', change apn and such.. Your bill will say, 'cellullar caller' , 'Tmobile user or tmo to tmo', it may also just say the devise's name. I've investigated this very issue on my own Tmobile bill earlier this year and those are my results. As to the specifics on how or why well, like I mentioned before, your phone settimgs as well as the device's settings of the party you are communicating with. Sorry, if my answer wasn't very straight foward. Hope it helps, though.
