I answer every call I receive. I don't see why not. If they try to sell me something I just hang up. I have nothing to hide and for all I know it could be someone I know calling me.
I did have a really strange call the other week on my phone from a number in Israel (looked it up online after), it was some bloke with really loud music in the background yelling something.
At first I thought it was someone I know from Sweden so I asked, "Is that you Andreas?" and they hung up.
I later asked him if it was he and he said it wasn't.
Didn't bother me though. Thought it was quite funny to be honest.