Ex-Samaritan here. I'm so sorry that we haven't been able to help some callers and I'm horrified by the negative experiences on here.
As PPs have said, it's a listening service - we're not trained counsellors, all we can do is be there when callers want to vent, or hand-hold through a tough time, and listen to whatever our callers want to say. Quite often, though, it felt like people phoned up who didn't want to talk, and would become angry and resentful if I asked gentle questions to begin opening up discussion.
It was incredibly hard. I dealt with all the issues outlined by PPs - men masturbating, prank calls, verbal abuse etc. But what I found most difficult were the calls where the caller was angry at the world, and therefore me. I found that with many callers, if I didn't say exactly what they wanted me to say, at the exact point at which they wanted to hear it, they would become sneering and angry. I realised that I was always walking on eggshells, second-guessing myself, to the point where I got my supervisor to listen in on some calls to make sure I wasn't doing anything wrong. I truly wanted to help people and often felt I wasn't. In the end she reassured me that I was doing fine and doing everything I could within the constraints placed upon us. I still felt I wasn't doing enough, though.
The calls when I truly felt like I'd helped someone made it all worth it, though. Some people would thank me and say they felt better for having released all the thoughts churning around inside. The call that most affected me was a lady who was very set on ending her life, was at peace with her decision, had absolute clarity on not wanting an ambulance, and just wanted a human voice to listen to as she fell asleep after taking some pills. That was so, so sad. There was literally nothing I could do.