I think that's silly. Do we really live in an age where we feel it's better to simply not communicate with people in the slightest?
Give them a call, you're not harassing them. If they choose not to answer or call back a voice mail number, then you can presume they don't want to be contacted.
Give them a call, you're not harassing them. If they choose not to answer or call back a voice mail number, then you can presume they don't want to be contacted.