By using NewSoftSerial (i.e. software serial port) you can have as many serial ports as you have digital pins (in theory). The main issue with software serial port is that the uP has to sample every single bit that the other end is sending, thus it can receive only one byte at a time.
If you read NewSoftSerial docs you'll also notice that the library itself must be used carefully when you have multiple instances of it.
HTH