Multiple serial ports & simultaneous communication

I have an Arduino Nano V3 which I need to enable communications between three serial ports. Data could come in any input line at any time, which needs to be routed to the other lines. There is an "AltSoftSerial" library which apparently doesn't work with the Nano...what options are available to me?

Add an external SPI interface dual or quad UART.
http://www.nxp.com/documents/data_sheet/SC16IS752_SC16IS762.pdf
http://www.nxp.com/documents/brochure/75017168.pdf