It can be done.
The Arduino Mega 2560 has more serial ports, and the SoftwareSerial can create serial ports on normal pins on the Arduino Uno.http://arduino.cc/en/Main/arduinoBoardMega2560http://arduino.cc/en/Reference/SoftwareSerial
It can be done in (many) other ways.
For example the very cheap 433MHz modules could be used with VirtualWire.
Every slave has to be an Arduino.http://www.open.com.au/mikem/arduino/VirtualWire/
An ethernet or wifi shield can turn the Arduino into a simple webpage.
So you could control the Arduino with any PC or a tablet.