I have an atypical hormone history. I have taken both T and E, and both of them seem to have strange effects on me, including some that are supposed to be impossible. My best guess is that my body must be very sensitive to hormones, so my experience may not be the same as most trans* people, but:
I had a very difficult time getting myself to a voice that was passable as male. It took years and years of trying. Despite T, I never had the trans/cis-male experience of voice cracking and breaking downward. Only in my last few years of living as male did I manage to mostly (maybe 70-80%) pass as a guy on the phone.
On E, however, my voice changed fast. It took about a week or so before I first had someone comment on my voice pitch seeming different. I went through a period of time that people described as male voice cracking in reverse, where my voice broke upward. Now, even when I want to pass as male on the phone (like to call someone about a purchase from a long time ago), it is simply an impossibility. I've tried. And it has created some awkward situations for me. People say that my voice is now quite different from where it was. A transwoman once sat in a group with me using a pitch measuring app and then p, afterward, came up to me and informed me that my fundamental voice pitch is a B3, if that is helpful in explaining. I guess I have somehow gotten my high school/college voice back, or at least something like it.
It has been suggested that maybe while living male, I managed to train my voice to sound lower, and that now I am just back to my normal speaking voice. I guess that could be true.
But it has also been suggested that this was truly a reaction to hormones. Because I did have that voice cracking period, and I can no longer produce male sounding tones, I tend to think that it was the hormones that did it. And if I'm right, then that means it is at least possible for voices to change quickly and drastically because of hormones even after T. Of course that's not to say it is common.
