Hey,
I am working on a prototype where I basically want to transmit the exact same message string from 1 Tx to all the Rx that are in range/can possibly listen.I chose RF because it is relatively straightforward and simpler than WiFi.Since I want the exact same message to be sent to every module, can't I just give them all the same address and make them listen on the same port/freq? Or is there a way I can tell the Tx to send a common message that will be received by every Rx, even if their addresses are different?
Yes, you can have all the slaves listening on the same address. Be sure to turn off auto-acknowledgement or all the acknowledgements will cause garbage. If none of the slaves does auto-ack it must also be turned off for the master. Or (I think) you could leave auto-ack working on the master and on a single slave.
If the slaves have different addresses then the master will need to send a message to each address in turn.
Thanks a lot! I had been scratching my head over how to go about using WiFi multicast for this implementation until I finally thought of RF transmission!
No problem. As long as you disable the Ack you can go up in high numbers..
Did a project with 600 slaves.. 
Made an error checking in the receiver that if something goes bad that it rejects the message..