Actually, I find cellphones are somewhat liberating in this regard, because they make it much easier to screen thanks to text messages.
If somebody actually calls me, I've no way of knowing whether it's important or not until I've already picked it up. But if somebody e-mails or texts, you can read it and decide there and then, without the pressure of the other person's "presence", whether you want to attend to it now or later.
I do know a guy who refuses to use cellphones, so any time he has anything to say, however trivial, he calls me on my landline and then tries to detain me for long periods once he has me on the phone. I find this very irritating, and most of the time I just fob him off, because I'm too busy (even sometimes "busy doing nothing") to sit there talking with him. But if he just texted me his "amusing thoughts", I'd appreciate them more and reply with a text of my own, whilst still being able to get on with other things.