Current mobile instant messaging (IM) applications offer limited information on the availability status of IM users, particularly, their availability for reading and responding to IM messages. Research suggests a gap between what IM recipients want to disclose and what IM senders want to see to determine when to initiate a conversation. The advancement of IM users' receptivity prediction makes it possible to present IM users' predicted availability status. In this research, we conducted user enactment, a design approach for researchers to let participants experience and reflect on possible designs of future technologies, to explore designs of IM availability status in 72 IM conversation scenarios. We explore how IM users interpret different presentations of an uncertain IM status from both the senders' and recipients' perspectives, and what they need and will act upon these presentations.