This paper starts with a preliminary theoretical research model which is developed based on the Unified Theory of Acceptance and Use of Technology (UTAUT). A number of qualitative methods, namely brainstorming, focus group and individual interviews, have been conducted to evaluate, select and validate the existing factors, as well as introduce new factors, to identify only the most related factors to be included in the preliminary research model. A survey questionnaire has been developed and validated to survey general users of the Smartphone in Saudi Arabia. A web-based survey has been designed and sent through email to 5,000 randomly selected smartphones users in Saudi Arabia. Data has been statistically analyzed using Structural Equation Modeling (SEM). The results indicate that performance expectancy construct, effort expectancy construct, brand influence construct, perceived enjoyment construct and design construct have a positive and significant relationship with users' behavioral intention to adopt and use smartphones in Saudi Arabia. Also, the results indicate that social influence construct has a significant and positive relationship with use behavior or actual use of smartphones in Saudi Arabia.