Calling is a funny word.
This is Dean, and this is just my personal observations.
I think most people “called” feel like it´s not such a good thing, but it really is.
Bottom line, it isn’t a decision. 
It´s what you have going on inside you, directed from God. Churches all have one thing in common to me. They all give me a back ache, and to be frank, they kind of bore me. I love praise and worship, but after that, I´d rather just hang out in the car, read the Bible, pray, wait for my kids, listen to a christian preacher on the radio, and come back in for the fellowship afterwards. I am a fellowship junkie. I love kabutzing. Nothing negative, just truth.
I love to help others, I need to help others. When they hurt, I am in agony. Some people have that (it´s almost a curse, ask my wife and kids). Other people like churchy stuff. We´re all different, God has a call for each of us. Some people can travel to third worlds and thrive. Some spend their whole time on a toilet. (well,as gringos, we all do tons of toilet time) but it affects people in different ways. Some get angry, some think it´s funny. When a street kid throws a rock at me or gives me the finger,i think it´s funny. Others don´t.
God uses all of us for different things. If you don´t absolutely LOVE what you do, and are completely miserable doing anything else, you NEED to check your calling. People that sold cars with me can tell you that THAT was NOT my calling.
Thank you for helping US to help others.