Gosh, no on both accounts. I think it's a horrible thing to do. You might worry someone needlessly or cause them to feel bad about themselves. It doesn't take that much effort to make a phone call. You don't even need an excuse...just the decency to let someone know "I can't make it".
Now, if you did it by mistake because you forgot you were supposed to be there, that's a little different, as long as it's not a habit, and you let the person know you didn't mean it.
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