This question betrays an assumption I wouldn't be hasty to make: that God doesn't call people to prophecy now. Certainly classical biblical prophecy has a closed membership. It's tempting to say prophets ended when the Bible did, but that implies they were fixtures of the biblical period, which they weren't. Prophets occupied a narrow niche of Bible history from the 9th to the 4th centuries B.C. No distinct office for prophecy existed earlier, when patriarchs and elders led their tribal communities. Prophets appeared when Israel's priesthood and monarchy were up and running to balance (and apply brakes to) those institutions when necessary. Prophets so often contradicted those in power that they seem like professional protesters camped outside the gates of government and organized religion.

This stance may have led to the demise of their role after both kingdom and Temple collapsed during the exile of the Israelites to Babylon. After Israel returned home, the office of the prophets was never quite the same because the institutions they addressed weren't either. The monarchy of Israel never recovered—unless you count the Herodian kings, which most Jews didn't. The priesthood got back on its feet for a few centuries before the second Temple was destroyed in 70 A.D., which ended it. In those waning centuries minor prophets plied their trade of speaking for God, but they gave way to another group of truth-seekers known as sages, who produced the Wisdom tradition (including the biblical books of Proverbs, Sirach, and the Wisdom of Solomon, among others). The role of the sages eventually morphed into the Sanhedrin. The voice of challenge ceased to be heard.

Yet the New Testament holds traces of that voice: in John the Baptist, who looks and sounds like Elijah; in Anna, who inhabits the Temple and is an early evangelist of the child messiah; and in the casual mention of Philip's prophetic daughters in the Acts of the Apostles. In fact, traces of prophetic speech and action have surfaced in every generation since that time, though the title has been retired. The ancient prophets were men and women who believed they spoke for God. Do we imagine that God has nothing further to say to us?

Scripture
Ezekiel 3:17-21; Matthew 23:29-34; Mark 13:9-13; Luke 13:33-34; 21:12-19

Books
The Prophetic Imagination by Walter Brueggemann (Fortress Press, 2001)
Four Modern Prophets by William M. Ramsay (John Knox Press, 1986)