Let's look at the texts.

Acts 2:4-11 - The Greek term in 2.4 is heterais glossais: "other languages." They were speaking in known human languages other than their native tongues. Verses 6, 8, & 11 show that human languages are meant.

Acts 10.46; 19.6 - It's not really explained what is going on here, but interpreters seem to think it was some kind of ecstatic language rather than a known human tongue. It doesn't make much sense they would be speaking in another human language not native to themselves. Robertson says, "It was not mere gibberish or jargon like the modern 'tongues,' but in a real language that could be understood by one familiar with that tongue." Robertson also continues, "In Corinth, where no such variety of people existed, it required an interpreter to explain the tongue to those who knew it not. Hence Paul placed this gift lowest of all. It created wonder, but did little real good. This is the error of all who have tried to reproduce this early gift of the Holy Spirit that was clearly for a special emergency and that was not designed to help spread the gospel among men."

1 Cor. 12, 13, & 14 - Again, this seems to have been some kind of ecstatic language (the "language of angels," 1 Cor. 13.1). The same word is used as was used in Acts for known human languages. Paul is just using their common term for "language." Some, however, are of the opinion that 1 Cor. 12.10 is about other known human languages (some people have a gift for language), and that it doesn't do any good to speak in, say, Russian if no one in the room can understand it. You need an interpreter.

There are basically 3 theories about the languages of, say, 1 Cor. 12.10 or 28:

1. Antiquated, foreign, unintelligible mysterious utterances. Gibberish that can be interpreted by someone God gives the gift of interpretation to. Sort of, I guess, like one computer knowing how to undo all the security codes that come from another computer. It's all gibberish to me, but a computer can do it.

2. Marvelous heavenly languages, the languages of angels.

3. Human Languages that are unknown to the speaker, as I as suddenly launched out speaking Swedish. The only Swedish I know is from the cook on the Muppet Show. : )

It's almost impossible for us to know what they were doing.

1 Cor. 14 - Paul didn't seem to have much interest in heavenly languages. He doesn't seem to think they accomplished much of anything.

14.2 - Speaking in tongues was only of value to the speaker and went no further. Some still believe this was foreign languages unknown to the speaker (which is possible). In either case, the ability to speak like this was perceived as a legitimate sign of God's indwelling power.

14.4 - The person who speaks in a tongue only benefits themselves. But for this to be true, the speaker must have understood what he himself said. Then why bother?

14.5 - Paul admits that the gift of tongues is important and not to be undervalued.

14.6-9 - But then Paul says, "Why bother? It would be more beneficial if I spoke in a language you understood." Benefitting others is his primary motivation.

14.13 - If there is no interpreter, stop. There's no sense if no one understands.

14.15 - Paul is distinctly in favor of using your mind in prayer rather than just languages no one understands.

14.18 - Do we interpret this that Paul knew many languages, or that he spoke in ecstatic languages? Know one knows, and it is interpreted according to how people WANT to see it.

14.19 - The object is to be understood so people learn, not to exercise a gift so people are impressed.

14.22 - Tongues were a sign of divine presence. Some still think it's talking about foreign languages. Hodge says, "The meaning is, that when a people are disobedient, he sent them prophets speaking in their own language. This is the natural conclusion from the premises contained in v. 21. When the Hebrews were disobedient, God sent foreigners among them; when obedient, he sent them prophets. Wherefore, the, unintelligible teachers are for the unbelieving; those who can be understood are for the believing. This view is also consistent with what follows."

You're probably catching on. It's pretty difficult to sort out because we don't really know what they were doing.

So, I was about to make a comment about tongues, but I read a few verses to make sure my comment was correct, and I was both wrong and became a bit confused as to the phenomenon.

I have only ever gone to mainline Churches, never been to any Church that engaged in the practice of tongues, let alone hear a pastor talk about it(outside of a reading of Acts), so what I understand is mostly from scripture. If anyone has personal experience with the phenomenon I would love to hear it.

But,

I am rather confused as to exactly what it is. I know that my parents went to these sort of churches when I was young, and they may have mentioned it before, but never was it explained in depth. From what I've heard and/or read from other Christians, it involves kind of letting a spirit wash over you and then letting lose your tongue and freeing what ever comes out. To anyone else listening to what proceeds, this may seem like gibberish.

Now as to scripture, as I am aware, tongues is mentioned in three places. Primarily Acts and 1 Corinthians, and briefly in Mark 16:17. I'll post the relevant verses in a reply, but paraphrase my understanding in this post.

In Acts(ch 2 primarily)
The event is described as the Holy Ghost coming into the Pentecostal Church, and they began to speak "as the spirit gave them utterance" to the people of various nations there. They were astonished because there was a wide variety of nationalities there, and they all heard in their native tongues from the mouths of Galileans.

So here, the Spirit fills of these people, guides their speech, and people hear and understand in their native tongue.

However,
In 1st Corintheans 13 - 14 Paul speaks in judgment of the Church of Corinth. Here they speak in tongues, and it unintelligible to anyone but the speaker to God. Paul describes this as only serving to edify one's self, which is not of good to the Church for our main duty is to edify one another rather than ourselves. He says that it is far better to speak 5 words in understanding rather than thousand without.
Also there is a distinction between these private speaking of tongues, which give thanks to God between the speaker and Him, and speaking in prophesy which others understand and serves those who hear them. There is a hypothetical posited by Paul saying if a whole church were to see a congregation speaking in Tongues, they'd think they were Mad, but if they were a whole congregation prophesying, they come to hear and understand.

Thirdly, Paul mentions a practice of separating into groups of 2-3 when speaking tongues, so that there may be one who understands to interpret.

So,
After having said that, it seems to me that the two phenomenon between the two books are separate occurrences that are translated with the same word, and that prophesying in 1Cor. is more similar to the Tongues of Acts, than the tongues of 1Cor. to the tongues of Acts.
That is my opinion/understanding, but I am open to understand what others might understand about the subject, and I am especially interested in testimonies of those who may have experience these things.

What do you think?