Yeah, and 2 + 2 = 5...Idiot
It's important but not THAT important. As long as you sound like 95% of the population does--and by this i mean you aren't absolutely painful to listen to--then you are fine. If you aren't, well it isn't that hard to change the depth/tone of your voice. It can be trained just like any muscle in your body can. It's just, nobody really cares to give it a shot.
Advice:
1. Invest in a tape recorder. Grab a kids book with some easy-as-sh1t sentences to read aloud. Say the sentence in your normal voice first, and STORE THIS AUDIO CLIP AWAY. Use this as a reference, or a starting point. Practice saying the same infantile sentence over and over again, trying to change your voice tones each time. Work up to afew sentences, then read something the length of a newspaper article to yourself, holding altered voice.
2. Buy a book on it.
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You always have to be conscious of what you are articulating when doing this. Like riding a bicycle, at you have to be aware of what you are doing at all times, eventually it becomes natural and
subconscious.
Give it two months of daily exercises(example: read a chapter of a book every night, aloud just before you go to bed.) and one morning, you'll wake up and scare the pants off yourself with how you're talking