Purpose: This study aims to generate empirical insights into the extent to which ChatGPT, a highly capable AI chatbot building on OpenAI's GPT family, is perceived and leveraged by EFL learners beyond the classroom. Design/Methodology: This quantitative cross-sectional investigation draws upon the technology acceptance model (TAM) as developed by (Davis, F. D. 1989. "Perceived Usefulness, Perceived Ease of use, and User Acceptance of Information Technology." "Management Information System Quarterly" 13 (3): 983-1003) to conceptualize EFL learners' attitudes, intentions, and actual behaviors of using ChatGPT in their informal digital learning of English. A total of 405 EFL learners answered the revised TAM questionnaire with scales including Perceived Ease of Use, Perceived Usefulness, Attitude, Behavioral Intention, and Actual Use. Findings: The results of structural equation modeling analyses indicated that while Perceived Ease of Use fails to predict learners' Attitude directly, it can influence Attitude through the full mediator Perceived Usefulness. It was also found that learners who take positive attitudes toward the usefulness of ChatGPT tend to demonstrate a higher level of Behavioral Intention, which positively and strongly predicts their Actual Use of ChatGPT in English learning outside the classroom. Originality/value: This study provides empirical evidence that supports the potential of ChatGPT as a powerful language-learning tool that EFL learners should utilize to participate in the ecological CALL creatively and productively.