I’ve been studying voice for a long time and I absolutely love it, but I’ve heard that piano is more important to study in high school if you’re interested in majoring in music (which I am, vocal performance) since choir will prepare your voice. I can’t take both and I don’t want to give up my voice lessons, but I don’t want to hurt my chances by not knowing piano.
Having the ability to play the piano will help you tremendously in music school. It will probably be a required course towards your degree, and it will also help you out with music theory.
There is a very good chance that your voice teacher also teaches piano. Talk to him/her about your desire to major in music, and ask if it might be possible to use a portion (maybe 1/3?) of your lesson time for piano lessons. This would be a "best of both worlds" situation for you!
Best of luck to you!