Supposing to have differents mobile devices (Android or IOS) connected to internet by the same Wi-Fi network, is it possible send in somehow a sms to all devices connected without have a particular application installed on the device ?
Like a simple sms in "broadcast"...
Is it possible do the same thing with a 3g connection instead a Wi-Fi network ?
Not directly, no. You would need to broadcast a wi-fi message to all the devices on the local network; your software would need to be running on those devices, and you'd need to respond to the wi-fi broadcast with the phone number of the device. Then you could SMS to those numbers.
What are you really trying to solve? This seems like a strange request.