About that phone call and the ending: Spoilers alert

I believe the ending meant she didn't care anymore one way or the other, whether inviting a new lover in or death. When the stranger was entering her room we heard in flash back Paolo's prediction that she would end up with her throat cut like so many others like her. Perhaps this was the very man who had been committing those other murders. The man she threw her keys to. We also heard a flashback of her saying she didn't care if she died in a few years. In her mind she believed she might be able to hold on to Paolo that long before she was too old or the money ran out and he left her. Since he left her years ahead of her schedule she decided the time to die was now instead of later. I do wonder what would have happened if she had reached her friend on the phone who had just left minutes earlier for NY. Would she have left with her? If so the implication is that she was not ready to die.

Either way, taking a new lover or inviting death, the ending showed Mrs. Stone no longer cared what happened to her. I usually don't care for endings that leave it up to the viewer, in the case it was fitting.