Well, I am not sure what you are saying.
God certainly is the same yesterday, today, and forever.
My question would be, why do we not see evidences of tongues being used in the OT?
It was a new event at Pentecost.
Actually, if one understands the typology, what happened was pointing back to a couple of different events in the OT.
One is the tower of Babel, where God confused man's language. Pentecost was, in fact, a reversal of this situation. The Church is a new humanity where mankind is reunited, but instead being united in rebellion against God, they are united in praising God. Men of every nation.
The other is Mount Sinai and Exodus 19-20. In Exodus 19-20, God gave his law to ancient Israel, but it was accompanied by a terrible display involving fear and gloom. The Law served a ministry of condemnation to the unconverted Israelites, because they were unable to keep it without being joined to Jesus, and the Holy Spirit. At Pentecost, God gave his Holy Spirit.
Both were accompanied by similar physical manifestations, but instead of the fire landing on the heads of the people, the tongues of fire lighted on the heads of the believers. This pointed to a sign that would tie the Jerusalem believers at Pentecost with the various different other groups mentioned throughout Acts which were later saved and spoke in languages just like the Jerusalem believers. Additionally, the believers often had hands laid upon them by the apostles, in order to convey this gift, to point them back to Jerusalem and its authority over them. God did not want an exclusivist Samaritan church, for example..he wanted them (and the apostles) to realize that they were all one body.
I can't make sense out of charismatic jabber concerning tongues, but I can make sense of these explanations. In fact, they are thoroughly biblical.
However, if you want to research the source of modern day "tongues", you will find them with this crazy young woman who started it all.
By the way, charismatics have changed their story over and over again..as soon as it is proven false. For instance, their story originally was that this was the "latter rain" and that God was giving tongues to preach the gospel in one final end-time revival. Well, since their tongues didn't match any known language, they changed their story and claimed it was a prayer language. So, they have changed their story over and over again as soon as it is proven false.