In response to an increase in both team collaboration and real-time dynamics in the current business environment, more and more companies adopt instant messaging as a means of improving team effectiveness and efficacy and reducing delays in decision making. This study offers a novel exploration of co-workers' we-intention to use instant messaging for collaborative work by investigating two group-level determinants - group norm and social identity - and considering the mediating effect of desire. A survey (n=482) was conducted to test the differences between high and low experience respondents. The research model explains 57.5% of the variance in we-intention. Research results show that desire partially mediates the effects of group norm and social identity on we-intention. The relationships between group norm and desire, as well as between group norm and we-intention, are found to be stronger for low experience group, in contrast, the relationships between social identity and desire, as well as between social identity and we-intention, are found to be stronger for high experience group. Implications of this study are provided for both researchers and practitioners.