We propose a User-Usage model to describe and predict (Technology) Adoption of Information and Communication Technology (ICT) by the users who have been significantly disadvantaged in terms of the capabilities to access, learn and use ICT artefacts and, at the same time, could benefit from them. We have termed this class of users as the 'Emergent Users' (EU) to signify the hope absent in the terms such as 'poor', 'low-literate' et cetera. We define Technology Adoption as initiation, learning and sustenance of usage. It is appreciated that ICT could benefit the EUs in many ways. However, an ICT intervention may not reach its potential if Technology Adoption is inadequate. The User-Usage model is a two-dimensional categorical matrix. Depending on the user-related factors such as Age, Gender et cetera, the 'placement' of a user in the User-Usage model could be decided. The vertical dimension of the model represents the six User Types - the archetypical categories of the users based on their usage patterns. Basic Users do only the tasks that require one or two presses of hardware buttons. Navigators can navigate the menu hierarchies. Text-Inputters can type text. Savers can follow, design and manage the directory structures to save files. Account-Holders can use account based applications to manage online identities and communicate with other accounts. Transactors can buy things online. The User Types are arranged in the increasing order of the ability to deal with task complexity. The horizontal dimension of the model comprises of the Stages of Usage - the typical interaction behaviours. The Stages of Usage are acquired as part of a user's journey in acquiring the skills for using an artefact. The journeys are interspersed with the barriers that a user may face. These are four in number - the barrier of non-exposure to ICT, the barrier of task-complexity avoidance, the barrier of low frequency of usage and the barrier of inability to form adequate mental models. A Stage of Usage lies between two adjacent barriers. The five Stages of Usage resulting from the barriers are Unexposed, Novice (cannot deal with task complexity), Rote-Learner (memorise task as a recipe), Fluent (same as Rote Learners but have done tasks frequently enough, so exhibit better command) and Competent (have adequate mental models, so can put their knowledge to new situations). The Stages of Usage are arranged in the increasing order of the difficulty of the barriers. The placement on the User-Usage model would inform about Technology Adoption potential of a user both quantitatively and qualitatively. The rules of the placement of the user on the User-Usage model were arrived through field studies involving rural and semi-urban EUs across India and their qualitative and quantitative analysis. Age, Education level, Gender, Proactiveness (motivation to use ICT for its own sake) and Time (total time since the first use of ICT) have been found to be the significant factors in determining both User Types and Stages of Usage. The fact that these are readily available for a population in the form of the census data helps to make a prediction about the number of people belonging to the different User Types and Stage of Usage. We have demonstrated that by using the data from the 2011 census. We have also used the User-Usage model as an analytical lens to understand the widespread Adoption of WhatsApp among the EUs in India. We have found that WhatsApp has challenged the User-Usage model by helping the Navigators among the EUs accomplish complex tasks of managing an 'Account'. These tasks include establishing social online identities, managing off-line communication, sharing and forwarding content, and creating and joining groups. At the same time, we have also realised that WhatsApp acts like an exception to the rule because it is only through design-innovation that the barriers posed by the complex tasks needed to operate accounts could be circumvented by the EUs. Through this exercise we were able to identify the design principles which could facilitate the EUs overcome the barriers of Technology Adoption.