Is it possible that you are conflating two different 90's TV shows? I can think of two shows that both match parts of what you said, but not all. As they are similar shows, similar tone, and aired around the same time, I wonder if you're just merging the two into one hybrid in your head?
Out Of The World (1987-1991) is a show about a half-alien teenage girl living with her mother on Earth. In particular, she talks to her alien father telepathically through a strange "cube" device:
Evie is able to communicate with Troy through a special "genetic" communication device known as the "cube", which he gave to her when she turned thirteen. The cube effectively functions as a telephone line to Antareus — it can even be used to leave Troy an "answerphone" message, as seen in the episode "My Little Evie". There are no controls on the cube; Evie simply calls for her father and the cube activates when he answers, deactivating when he "hangs up". Sometimes when Troy uses his powers whilst talking through the cube, a beam of energy is emitted directly from the cube.
Unfortunately, Evie had long blonde hair:
Small Wonder (1985-1989) was a TV show about a young girl who was actually a robot, built by her "father", to act human. I don't remember her voice ever changing, though she was a robot so I guess there could have been episodes where she had voice box problems. But she was a young girl with short dark hair: