but I keep missing opportunities
You don't miss opportunities for not answering the phone. You should still receive them once the phone stops ringing.
i can second this.
i have the same problem with one of my sims. never missed an opportunity though.
for me it looks like the problem is connected to space, you have to roam. often, if not always, my sims tries to look for rather large free space before he answer the phone.
probably he does so to not block some other sims way, even if there isn't one.
so leaving the "crowded" place is most of the time a solution, although not a satisfying one.