Ministry calling is a call to vocational ministry.  This is a life-long call, but the context of the ministry itself may change.  We see this frequently in pastors who change churches or youth ministers who become senior pastors.  The people, age group, church, or style of ministry may change, but the calling remains the same.  

When looking at where God is calling you to ministry, there is a quote by Fredrick Buechner that comes to mind:

“The place where God calls you is where your deep gladness meets the world’s deep hunger.”-  Fredrick Buechner

We need to find where out deep passions and desires meet the hungers and needs of the world and that is where we need to minister.  I think that over time our place of deep gladness in ministry roles may change, but there will always be a new hunger and need to go along with our new passion.