If you go to the plans page, you will see that there isn't an unlimited incoming call row in the $10 plan (compare it against the $15+ plans which has this). So, incomming calls will be deducted from the 50 minutes you get
Nope. I'm with mimmo. The add-ons cover incoming. It's only texting that is the real limitation. But there are work arounds.
Maybe some day someone can test whether a US caller will use the 500 after plan minutes are used. I'll test for that the next time I'm out of the 50. But then I also still have some 200 left so it might just use those minutes.