We use google calendar at our company, and I have some of my colleagues calendars shared with me. This is very convenient as I can check their availability right from my phone when, for example, scheduling a meeting. What I miss is a very simple feature. If I am about to call somebody and his calendar shows that he or she is in a meeting right now, I would like my phone give me a quick warning:
"Alex seems to be in the meeting with Joe for next 40 minutes. Are you sure you want to call him?"
[YES ] [no] [Remind me in 40min]
If somebody would write an app doing that I will be one happy user!