I just assumed they were all yawning because it was late 
Consider yourself lucky. My mother-in-law gets up at dawn every morning to walk and thinks nothing of calling us any time after about 6 am. Then she acts a little shocked that I’m still in bed. I’m one of those people, though, who has no problem ignoring a ringing telephone and I figured out after the first few times it happened that it wasn’t going to be anything important.
We stick to the 9 pm rule, but it wouldn’t bothered me if someone called me up until about 10 pm, as long as they weren’t expecting to have some long conversation.
For just about anyone that I might be calling I wouldn’t think twice about calling after 9pm. Normally to ask if they feel like going for a beer. If I’m calling my parents, I’d call up until about midnight. They tend to stay up pretty late, and if I’m calling them chances are pretty good that I actually have something to say. If I’m calling someone I don’t know, it would most likely be during the day, but I guess I probably wouldn’t call after 9pm.
In the mornings, I wouldn’t call before 10am or so. But, that is just because I’m not up before then.
As for people calling me, whenever is fine. If I’m sleeping or don’t feel like answering I won’t. My phone is always next to me by my bed, so if I wake up (unlikely), I’ll just check who it is, and almost invariably ignore it. Although, there have been times I’ve been woken up and convinced to get up and go drinking.
Most of this is pretty irrelevant to me personally though seeing as I almost never call anyone. I don’t call just to talk…
9 pm is a pretty good rule, unless you know the person’s schedule/habits.
My parents are in bed by 9 pm, but up by 5 am. I’m just getting home from work at 9 pm, and my parents know not to call before 10 am.
I’m at the age where my friends are starting to have kids, which means there is no “good” time to call, but I won’t call late (say, after 8 pm or so) because that’s “mom and dad” quiet time for most of them. However, I also have friends that I wouldn’t hesitate to call at 2 am.
Don’t call me after 9, don’t call me before 9. In fact, don’t call me at all if you can avoid it!
I hate the phone, and have learned a long time ago that just because it rings, nothing is making me answer it. I screen all my calls unless I’m expecting someone. Once a week I call my aunts.
I’d much rather talk in e-mail or in person. Most of my friends are the same way. In my case, at least, three years of customer service will do that to you.
If the phone rings after 2am, it better be an emergency or a booty call.
I always have the ringer turned off on my bedroom phone. If I’m awake I’ll hear the phone ring in my living room (or notice that the display on my bedroom phone has lit up). If I am asleep, you can not reach me by phone, period. No need for rules about time in my case. 
To avoid the obvious question, in my particular case I truly can not think of any possible theoretical emergency that would involve phoning me that wouldn’t “keep” until the next morning.
I work a rotating shift roster. Any time is a bad time to call, because I’m asleep at different times each day.
If I’m not working I’ll accept calls up until about ten thirty to eleven PM. Himself’s family are in the UK, so sometimes the timezones get a bit mixed and they call at a time that would be a bit late for most people. But we’re both usually up at that time, so it’s cool.
What I don’t accept is calls before nine am, unless something’s desperately wrong with one of my family. Unless I’ve gone to bed early, then nine is usually the earliest I’ve gotten up and anything before that will wake me up and I will be grumpy.
Don’t call me after 3a or before 9a. I’ll push it to 4a or so friends, but the 9a start time is non-negotiable. I will not panic if the phone rings outside these hours; I’ll just be irritated.
However, I will not call someone else’s house with a shared phone past 10p nor before 9a. All my friends have cellphones, though, so it’s not usually an issue.
When I was growing up, 9pm was always the late cutoff for anyone who wasn’t ultra-close friends or family. These days it seems to be 9:30 or 10pm more often, though - mostly because of cell phones and the fact that pretty much everyone has free minutes after 9. If a call would normally cost money or minutes (long distance, cell plan, whatever), and it’s not really urgent, 9:05 is a much better time than 8:55.
If you call me when I’m sleeping, you just aren’t going to get me; my cell is off when I am sleeping, and I will quite blissfully sleep through the ring of the home phone in the next room.
9pm is the generally accepted standard among my friends who keep relatively normal daytime schedules. Anybody who knows me well enough to have my cell phone number, on the other hand, knows that if I’m asleep before 1:00 AM, I’m either sick or I’ve been drugged. They also know that I get free minutes after 9pm. They are then wise enough (this being a prerequisite for obtaining my cell phone number) to combine these two knowledges such that I receive 95% of the calls I actually wish to receive between the hours of 9pm and midnight. It is a thing of beauty.
Anyone who has my phone number knows they can call me (unless I forgot to tell them) just about any time between noon and whatever time I go to bed. If I’m awake before noon, it’s because (a) I have a class and therefore can’t talk to you anyway or (b)I am doing something else which requires me to be awake early and probably would not make good conversation anyway.
My mother likes to call me at eight in the morning on weekends to wake me up and gripe at me for not being awake already.
My mother dislikes anyone calling after 9 pm. Dad doesn’t care, but you don’t want to call him after that, or any time really, because the man won’t talk. He just holds the phone and breathes.
I just had a phone conversation that lasted from 9 pm to 4 am.
But I’m odd.