How Avraham was able to receive the Divine Presence if he was not in Eretz Israel and had no brit milah?
God is all capable. He also revealed himself to Yechezkel outside Israel and Bilaam who was a big rasha. I think it's just "normally" in israel in the "normal" spiritual system of prophecy. but just like God can perform miracles and override the normal physical system, so too He can do a miracle in the "normal" way of prophecy and grant someone prophecy even outside Israel
According to one of the opinions (I believe Rashi holds like this, contrary to the Ramban, according to whom it is a nice question), the prophecy in the beginning of parshas Lech Lecha ("go for your sake ... to the land that I will show you") was not the first one experienced by Avraham. Rather, the first one was the Covenant Between the Parts, which did happen in the Land of Israel.