Since the role and the availability of digital technology in society is growing, educators need to increasingly more often decide when and what digital technology to integrate into their teaching. Thus, those decision-making competencies need to be developed and measured especially for pre-service mathematics teachers. Therefore, we conducted an explorative interview study to understand the variety of argumentation and justification of pre-and in-service mathematics teachers on whether to use or not use digital technology in the teaching phases of Prediger et al. (2013), and what criteria they use in making those decisions. The analysis shows that (1) based on the arguments and justifications different level of decision-making competencies can be distinguished and (2) the recorded criteria on whether to use or not use digital technology are suitable for reflective practicing of such decisions.