The problem with the Pentecostal interpretation of this chapter is that they imply that an "unknown tongue" is a language that's completely unknown to anyone except God.
If 1 Corinthians 14 was talking about the ecstatic utterances of the Pentecostals it would be the one and only passage where "tongue" was anything other than a real, human language (or the organ in your mouth). Of course God provided a miracle at Pentecost and again in the book of Acts, but both those times the miracle was to allow men to speak in foreign languages for the furtherance of the gospel.
>muh heavenly language
>muh prayer language
<22 Wherefore tongues are for a sign, not to them that believe, but to them that believe not: but prophesying serveth not for them that believe not, but for them which believe.
So just as in Acts, tongues are a tool to spread the message to people who speak tongues strange to us.
I've visited a few of these churches myself and from my experience they usually view their babbling as a "sacrament" citing Acts 2:38 and implying "ye shall receive the gift of the Holy Ghost" refers to tongue talking.