That's a great question. I was thinking about it a few days a go.
Well, Beyoncé says "I misshu" in her song, I miss you. And I've heard native speakers - at least from the US - pronouncing this way quite a lot.
I've never asked a native speaker about this, so John's contribution may be more reliable, although I believe it's a matter of accent, and not about sounding educated or not.
These kind of statements always make remember about a topic I enjoy a lot, which has changed me a lot, which is: linguistic prejudice.