For long since the advent of electronic communication for the common people, Hindi and other non-English languages were encoded in Roman itself. So much so that Hindi encoded in Roman and not Deonagari, the official script of the language, has earned a character of its own and has contributed much to what is now being termed as “Hinglish”.

Defining Hinglish:
No definition of Hinglish can be given for sure. No surveys are present to show who uses it, and how much and in what context this is being used. Hindi/Urdu/Hindustani, all being written in Roman can be comfortably termed as Hinglish. Going by this definition, we can safely say that there is a lot text available online and much of it has already passed the electronic communication channel (through SMSes, mails etc.)

Users of Hinglish:
There is a lot of interest in 'Hinglish', particularly from the industry. Even though a puritan view would reject the whole idea of Hinglish as an aberration, this term is going to stick. And therefore, the need to study this behaviour of the people for the sake of academics as well.
Hinglish is being used both by the native speakers and non-native speakers of Hindi/Urdu/Hindustani. Hindi/Urdu/Hindustani has been traditionally written in Devanagari script or Urdu (Nastaliqh) script. But its Hinglish avatar is now being written in Roman. And this has only increased the users of this language. Now, the whole of South Asia can be said to write this, because Hindi/Urdu/Hindustani is the lingua franca of this region.