Everybody welcomes an 'open door' policy, but make sure you set some parameters to guard against constant interruptions.
PROTECT A CERTAIN TIME every day. Switch your phones off and close the door. There's no harm in sending a clear message to the world that sometimes you are strictly unavailable.
TURN ANOTHER TIME IN THE DAY into your 'open house'. Post the time on your voicemail message or on every e-mail.
DON'T RISE TO BAITS. If you hear a jibe about how hard you are to get hold of or how standoffish, just bounce it back with a 'maybe you're right'. They won't love you but they'll leave you alone.
LEAD BY EXAMPLE. Ask other people: 'Is this a good time or would you prefer me to come back?' Their time is valuable too.