I've never been granted permission via telephone or email. Check that.....once. It's a 4.5ac tract that's a pretty killer turkey spot....but my father in law knew the landowner (who lives 3 hrs from here).
I've never been DENIED permission when I went to ask face-to-face. I've got a little "system" I learned from a Joe Brooks book that works like a charm.
Sage advice given, above.