The earliest believers in Jesus were Jews and heir Bible was the Tanak, they were almost all literate as that was a priority with Jewish people to read and understand scripture.It is simply not true that they were illiterate, and wherever the gospel has gone throughout the pagan world, so also has literacy!
Few had a new testament. :)
Some people were literate and some were illiterate. This was before the invention of the printing press, and all that that implies.