Changing back to my old phone from my new one with T-mobile?

Hello,

I recently changed provider and moved with T-Mobile, which I am very happy with, however I don’t care for the phone. I would like to know if I can change my number over to my older Iphone and continue to keep the T-Mobile phone. Same number, same company, just wanting to return using my older iphone, which I am more comfortable with? Thank you.