Make Arduino and 89C52 talk to each other

I am trying to create a project in which I am required to make Arduino and Atmel 89C52 talk to each other.

I know this can be achieved via UART but the problem is my Arduino is already using its TX/RX ports. Is there a way to make them talk by any other means? Like I2C or SPI interface? Would soft UART suffice? The whole project depends on then talking to each other effectively.

Regards