Yes there were Jews and Christians in ancient Arabia. There were many Jews in Yemen, and there were the two main Christian states of the Ghassanids (Banu Ghassan) and Lakhmids* (Banu Lakhm) in Northern Arabia, amongst others. This was not only "Orthodox Christianity" but also Nestorian Christianity and other religions which existed around the Arab peninsula, the birthplace of many of these religions being Iraq.

You have to remember that the Prophet Muhammad was a trader/merchant by training, and his first wife, Khadijah, was the leader of a caravan group. As a child (Prophet Muhammad was an orphan, raised by his uncle) and later in life, in scripture and what can be logically reasoned, is that he, and many other Arabs traveled around Northern Arabia, into what is today Syria, Jordan, Palestine/Israel, to trade their wares. A big commodity was camels, that were raised in Arabia, and then sold to markets in the Levant.

There is even one hadith (story of the life of the Prophet), stating that a Christian monk met Prophet Muhammad, as a child in Syria, saying that he would be a man of God. Not sure how this hadith is regarded in terms of veracity (not all hadith are equal, just like not all gospels are considered orthodox), but someone else might be able to comment here.

So far from being isolated, the world the Prophet Muhammad was born into, was very well connected with the Indian Ocean, and with the Mediterranean and Iranian worlds. Mecca being a hub of trade, as it flowed up through Yemen.

*For a time

Sources: There is nothing here really outside of common knowledge, however there is a nice map in "The Great Islamic Conquests AD 632-750" published by Osprey, which lists the tribes and their religious affiliation at the end of the 6th century (Prophet Muhammad is thought to be born in 570AD). If you want to know more about something specific, I can try to find a good source.