Reminds me of my second job. I have a firm rule of answering phone calls only when I feel like doing so. I didn't feel like answering the call about the job offer over the weekend :). Still got the job.
The funny thing is, in general people tend to respond positively to you not being available every second of the day. Sometimes it backfires, but most of the time setting limits tends to 1) make you look busier, 2) signaling that your time is valuable to you.
Both tends to make people think you're more important and worth more, not usually make them strike you off their list and move on to the next person.
The exception would be really low level positions where they see people as interchangeable, but even then in most cases people have already mentally chosen you when they call, and not being available makes you more desirable, not less, so for them to move on they need to have cared very little to begin with.
... which is another reason to not be instantly available - I for one don't want to work for people who see little enough value in me to be prepared to drop me if I don't answer the phone 24/7 unless I've been contracted specifically to be available at any time (and you better believe they'll pay through the nose for that).
A lot of younger employees could do with learning to set boundaries, be unavailable and say "no", and experience how that can often get them a lot more respect and better job conditions.
