How late do you accept phone calls at night?

First, a little background: The other day MIL called DH at work to inform him that his 94 yr old grandfather with Alzheimer's is in the hospital because he cut his lip with scissors. He will be ok but they want to put him in a home. Later that night at 10:00, DH and I just sat down to watch SVU and cuddle when MIL's number comes up on the caller ID. We were both nervous so DH answered. Turned out she called just to BS and tell him about a photo she just came across. Are you serious? FIL (not married to MIL) calls late at night as well. Sometimes we are getting ready for bed but DH feels guilty ignoring their calls so he will answer.

We don't have any children or pets to worry about waking up, but my parents always had a 'no calls after 9pm' rule (unless it was seriously important of course).

So, just out of curiousity, is anyone else bothered by late night calls that can really wait until the next day? How late is too late for you?