As has already been mentioned, field service and especially phone witnessing.
I didn't do much phone witnessing when I was growing up in a rural area. But I did it a few times after I moved away from home to an area with high rise buildings. I just didn't like bothering people over and over again with things they were not interested in talking about. And phone witnessing really brought it too the fore. I try to follow a basic rule of human relations that some people think is unique to the Bible and refer to as the golden rule. I try to treat other people the way I wanted to be treated. And I know I hated to be bothered by telemarketers. When I used a landline, before I had caller ID, I'd just say "No" and hang up on them. When I got caller ID, I wouldn't even bother answering.
I once quit a job because I absolutely hated the cold-calling to set up a sales appointment. Then I moved and I had to try this phone witnessing a few time. I was completely ineffective with that method, which is actually a positive. Certain people might have the phone voice to make it work sometimes, but not me. I knew that I would not like it if somebody was trying to push some propaganda on me on the street, at my door or on the phone. So why was I bothering these people? It turns out the message isn't life saving.