I wanted to post again in order to offer some words of encouragement and a link:
I started working on my voice in late August. It's taken me until early December to develop the voice from the clip I posted above. I'm very good with it, but some days I have great voice days and other days I have decent days (that clip I'd say is somewhere between decent and great for me, leaning towards decent). And even though I'm always very passable with my voice, I'm still working at it and trying to get it exactly where I want it to be. It takes time, and I had to learn to become very comfortable with that fact before my progress really started to climb.
A lot of developing your voice is about forming the habit and being very familiar with how sound feels in your mouth. I know that must simply sound like I'm saying to practice, but to me, it feels like there's a greater element than that -- than just practice; it's something about developing intimacy with how you speak. The best analogy I can think of is how each musician plays his or her instrument in their own way, regardless of their level of expertise. They spend hours looking for the methods to play the sounds and tones that they like and that feels right to them, not just to play well, but to express themselves in their own eloquence.
Here's a link that a friend showed me yesterday. It's from a girl who's offering some tips on learning your voice. I really love her video because when I started out, I used many of the same ideas that she's talking about there. I think it's wonderful advice for beginners, and aside from just seeming like a very pleasant person, I feel she does a great job explaining all of it:
I wish you all continued luck in your endeavors!