I searched for a particular phone company and the results were T-SHIRTS. I can't imagine buyers are happy with the change. Is this an experiment or permanent change?

Thats probably, because SS doesn't allow brands in keywords, as far as I know.

Same here, few of my illustration are nowhere to find on shutterstock ("people avatars" no brand involved) and also no sales for a few days.Never experienced this before.

I just did a quick search - assuming you mean the company that starts with "T" - I got 95 pages of results no shirts and easily found one of yours on the first page. and there are others upon further scanning.

edit:
Did their Auto-complete function default you to t-shirt instead and you just didn't notice?

well that blows - for anyone wanting to buy or sell AT&T images.
Add the word 'phone' to the search it helps.