I did a little bit of Biblical research on speaking in tongues.
[by research, I mean that I asked my husband... he knows a lot about such matters :) ]
According to my husband (and to most Pentecostal churches that I've been to), there are two types of speaking in tongues mentioned in the Bible, although the text never specifically says that they are different... leading to our confusion in class as to how the babbling many of us have heard in churches is a reflection of the Acts 2 Pentecost story - and also to a pretty big theological debate.
The first type of speaking in tongues - "natural" or "foreign" tongues is what we read about in Acts 2. "They were all filled with the Holy Spirit and began to talk in other tongues, as the Spirit gave them power of utterance" (Acts 2:4). For the purpose of spreading the Gospel, believers were given the ability to speak foreign languages. I think this story is the only instance of the gift of foreign tongues in the NT.
Okay, so, the second type is "spiritual" or "heavenly" tongues, and this one is more frequently mentioned in the NT. Acts 10:46 - "for they could hear them speaking in tongues of ecstasy and acclaiming the greatness of God." This language does not appear to be understood by anyone, but is a tongue of ecstasy. The same thing happens in Acts 19:6, with the addition of prophesy. Mark 16:17-18 (the snake-handling verses) says that believers will "speak in strange tongues." 1 Corinthians 12-14 is where the most info about speaking in heavenly tongues is given. Paul acknowledges that some have the gift of tongues, and some have the ability to interpret them. He mentions speaking in the tongues of angels (but notes that it - like all things - is worthless without LOVE). In Ch. 14, he emphasizes that if tongues are not interpreted, they're gibberish. But, he also says that this is the language of prayer (verse 14), with which his spirit prays... which seems to say that an interpretation is not needed if one is praying alone in his closet a la Matthew 6:6.
(You can read more about this here: http://en.wikipedia.org/wiki/Glossolalia. Glossolalia is Greek for tongue-speaking.)
I wonder if the authors of the NT only had the first kind of speaking in tongues in mind... and church leaders have since constructed the second form of speaking in tongues so that some people could "shandalah" (it all sounds like that to me) and feel much holier-than-thou without having to have an actual miracle. I think you could very easily read the first type of tongue-speaking onto the 1 Corinthians 14 verses (interpretation is necessary), but I acknowledge that this is a MUCH bigger topic that I can fully explore in this blog. :)
So, I'll share a story. My husband and I used to go to a traditional, old school, Pentecostal church (don't even ask me why). And every Sunday morning, when there would be a lull in the worship, we knew it was coming: a little old lady would rise up out of her pew and say, "Shandalah... rahshahkosomarlaseeto... errahshambada"... and the pastor would get this expression on his face (as if he were receiving the word from the Lord), and then say something completely generic like "God wants us to know that He loves us and He is with us this morning. Hallelujah." And everyone would clap like a miracle had just taken place. They legitimated this process with 1 Corinthians 12-14... but, it seemed so obvious to me that this was no representation of a "spiritual gift" that Paul talks about: it was just a tradition, a way to make the congregation feel that God was there with them.
