Situation: I had a technical interview over the phone with a particular place and they want to set up to have me for an on-site interview, which would require air travel. At this point though, after considering things, I want to move forward with other opportunities. This so far has been coordinated through an HR person.
I've tried calling the HR person today three times, but have not been able to contact her. Since I have interviewed with this place and they're obviously interested in me, I would prefer to talk to them in person to let them know my decision. I have not left a voicemail. It sounded like they were hoping to get things set up for an on-site interview very quickly (either setting things up today (Friday) or the following Monday for a week from now) so I'm hoping to contact them today if possible.
At what point should I send an email informing the HR person of my decision instead of trying to contact her via phone?