Unless you are saving lives (a doctor) or protecting the country (in defense), or maybe a few other edge cases, the perception that you need to get back to a person in a few hours is probably more on your end than on the recipient's.
Or need to fix your production servers which have suddenly crashed and every minute of downtime is costing you money and reputation. A category many people on HN probably fall into.
Bingo.... you aren't as important as your cellphone makes you feel.
I have my funky cool blackberry - but I leave it on "Phone only", and, because I rarely ever answer it, hardly anyone ever phones me. I also have no problem ignoring it if it rings and it's not a call I actually need to take - I know it'll go to voicemail. The key is not letting the phone dominate your life. It's really there so I can phone people when I need to, or so I can allow someone to reach me when I need them to - and nothing else.
