Why do most Christians call Jesus "Son of God" rather than simply "God"? We call Jesus the son of God that became the son of man.  And yet, Jesus is God per the doctrine of the trinity.  Why don't orthodox Christians address him as God when talking about him and praying?  Is there a biblical basis?
Trinitarian Christians most often refer to Jesus by name or by the title of "The Son of God" to distinguish between the Three Persons of the Godhead.  (The title of "The Son of Man" is a specific reference to a prophecy in Ezekiel with which Jesus identifies Himself.)

The Doctrine of the Trinity can be explained as such:


Jesus is God
The Father is God
The Spirit is God
The Son is not the Father.  Jesus is not the Spirit.
The Father is not the Son.  The Father is not the Spirit.
The Spirit is not the Son.  The Spirit is not the Father.


Jesus had a specific role in that He is the One who became a man.  Neither the Father nor the Spirit did so.  So, we often reference Jesus specifically because of His role in redemption.

However, we may refer to Jesus as God and be correct in doing so.  Indeed, we often say the "God became a Man," and we mean by this that The Son of God became a Man--not the entire Trinity.

So, to answer your question, we don't refer to Him as God all the time, because we are identifying and distinguishing Him for His Incarnation, Vicarious Sacrifice, and Resurrection.  Yet, we can and do refer to Him as God at times--just not as often as we refer to Him by His Name or His titles.

See this question for more information on the Biblical Basis for the Trinity.