The impact of technology on society is clear and profound, but the influence of society on technology is more subtle. The wave of social media on mobile communication devices has hit the shores of many countries. However, the influence of culture on these technologies is less obvious. This is an empirical study about Twitter on a mobile communication device (TMCD) used in group collaboration, undertaken to ascertain and gauge the user group's subtler exhibitions and behaviors from two opposite cultures: western and eastern. To outline TMCD impact on group communication, a baseline of online message board (OMB), a common form of computer-mediated communication (CMC), is used in a comparative analysis. A total of 167 MBA and undergraduate students from the United States and South Korea representing western and eastern cultures participated this experiment. This study revealed a mixed result in the cultural difference between the two countries. In the TMCD category, the Korean groups exhibited 1) a significantly higher number of initiatory tweets and 2) a significantly higher number of tweets promoting group harmony by virtue of their agreement with each other. But the Korean groups failed to exhibit 1) a significantly higher number of friendly tweets, and 2) a significantly high level of pro-activeness by tweeting more to each other to accomplish the given task than the U.S. groups. The data analysis result and discussion are provided.