Being a web developer, I used to get a lot of calls from clients, so much that it got to be hard to work for me.
I remember looking into that and I'd have killed to get it, but it was only available in the U.S...
Other option is to keep two phones, one personal, one private.
But then people started saying that I was either not reachable or I ignored them.
I didn't get rid of my cell phone on purpose, just used the fact that it broke to not get another one, and it just works great for me.
Returning family calls, on the other hand...
I'm in Italy, and it wasn't just family and work, but all kind of random people... People don't like to use email, here, so they call you for anything (like your bank, landlord, whatever).
Also, then don't trust email: the thing that annoyed me the most was that the rare times they chose email, they would also call me to let me know they had sent me an email, to make sure I'd read it...
Go figure.
The real problem here is that the people contacting you do not respect your desire to not be on-call 24/7. In my opinion, this lack of respect is good enough reason to not feel bad about ignoring them. Put your phone on mute and stop letting inconsiderate people push you around. Or just continue not having a phone because that works too.
I probably didn't care about them, but I do care about keeping good work relationships.
I'm totally reachable. I have email, and Messages. The thing is just that I can decide when to check them, and they're less invasive.
Works for me. I use the standard iOS features to make sure important callers (eg. the children's school) can get through.
The trick to getting this to work is to be consistent. Don't tell people you are not reachable and then pick up their calls.
I always make sure to disable the auto-away setting in all chat/IM programs so it always shows me as online, and then I explain to everyone that since the program is not smart enough to know for sure that I am available, I prefer to avoid the confusion.
With phones I follow a similar philosophy: I make sure to avoid answering it all the time, I let it run out of battery, or in Silent mode, or I leave it at home, etc. and I'm very vocal about having done so.
I don't know if this makes me antisocial, but it seems to work fairly well in removing other people's expectations (except with my dad heh).
If they called me to see if I knew their password and I didn't help them they'd feel stuck, now they just go in their inbox, find it themselves, and go on with their lives without emailing me, which ultimately doesn't piss them off.
Before, I just couldn't handle the amount of calls and sometimes I just wouldn't even call back if I thought it wasn't important, then people would have to call me back to finally try to solve their problem. Now, I always reply to my email, so in this case, too it's better for them.