Originally Posted by Djokison

You are correct in that when arriving in the US, everyone has to go through immigration and customs. However, if on an international-international connection and arriving on BA, the luggage will not appear on the belt. You are required to go through all the same steps as everyone else, sans picking up/dropping off your checked luggage.

I've connected through MIA multiple times to int-int using AA/BA/AB and with AA and AB have had to always pic up luggage, with BA this was never the case. (Much to my surprise the first time, when I stood there for quite a while waiting for my luggage that hadn't arrived. It wasn't until I asked the BA agent about my bag, he told me that BA sends it through.)