Prior to the 7th Century, there is no record or at least no Roman ever visited, the interior of Saudi Arabia. While there were some references to cities which may have been Mecca, there is no record of it being any place of renown to anyone with the exception of the Arabs.

During the Byzantine period, which is what I think you're referring to, Mecca and the Red Sea had become and important trading point. Due to the Sasanian - Byzantine wars which disrupted the trade flow and the anti-trading attitude that the Sasanians had the route from the Red Sea had become important to continue the flow of spices. Here the role of Mecca as a hub for the spice trade had become to grow.

Whether or not the Byzantines ever visited the city is questionable. No source that is solely Byzantine ever refer to anyone going there. However, subjects and allies of the Byzantine Empire, such as the Arabs Christians, Egyptians and Ethiopians did know the place and referred to it as an important trading city.

This importance also played a part in the Byzantine - Sasanian war, called the Year of the Elephant, where the Christian ruler of Yemen asked the Sasanian Empire for help in defeating the Meccans because one of their tribesman had defiled the church that he had built in Sana'a.

During the time of the Prophet Muhammad, there are documents which exist which were written by fellow Muslims with Muhammad's message, to the Byzantine king Heraclius, the Sasanian King, and others inviting them to follow his religion. Whether they still exist or not I don't know, I would think that they would still exist, but there is documentary evidence that there had been documents written on behalf of Muhammad.

Sources:

• Encyclopedia of Islam: This is where references were given about the document sent to Heraclius are found in.
• The Arabs by Anthony Nutting
• The Arabs in History by Bernard Lewis
• A History of the Arab Peoples by Albert Hourani