There's a whole forum on the topic of voice, actually. (
https://www.susans.org/forums/index.php/board,346.0.html )
I'll give you the short version of what I learned there. To start with, there are many women who transitioned well after their 20's, who started with deep voices, who now sound quite female and are passable both on the phone and in person.
From what I've seen, it's really just a matter of practice and patience. First, you learn a little bit more about the human voice and how it's created physically. Things like where your voice is resonating matter a lot. Then, you learn ways to control and influence that. Then, practice, practice, practice. I hear it helps a lot if you use it 24/7. Eventually, it simply becomes second nature. After enough time, it takes more effort to revert to your old, male-sounding voice than to use your new voice.
So HRT won't help a huge deal, since the physical changes to your vocal chords are one-way, but don't despair. This is definitely an issue which can be addressed, which I'm confident you'll deal with successfully.
Sorry if that's off-topic. I do have a personal story here. I've always had about 3 different voices I speak with (that probably sounds kinda weird). The natural one is probably the most female-sounding one, and according to some of the forum members here, it's sorta close to passable. You can hear it, if you want (it's in the stickied thread in the voice forum). I don't really put any effort into any of them. I can't speak to HRT, but I can say you can consistently speak in a relatively higher frequency and with less chest resonance without it seeming forced or taking any significant effort, once you get used to it.
Edit: And by the way, you look 100% female judging by your avatar, and that helps a lot. Remember, people usually judge gender by their first glance at you, and unless the voice is really jarringly different from what they expect, they'll hear a female voice if you look female and sound even close. Remember, pitch falls within a range for both genders, so it's not a specific number you're looking for. I have no idea where your voice is now. But I'm guessing for you, with a little bit of practice to reduce things like chest resonance and bring pitch up a little, most people will still completely consider you female even if you have minor frequency or resonance issues. And with more practice, those will eventually mostly disappear.
