A lot of people don't really know what the gift of tongues actually is. Also, the term "baptism in the Holy Spirit" is not exclusive to pentecostals.
There are multiple people of all denominations who are filled with the Spirit, and choose to, or not to speak in tongues.
Speaking in tongues is not a miraculous gift that enables people to speak in some kind of special unlearned language, unless people are inspired under the power of the Holy Spirit to speak a known language for a specific purpose.
Basically, a person will speak in tongues when overcome by a moving of the Holy spirit within, in such a way that what is flowing out of you from within cannot be expressed in a human language, because of the limitations of the language, and the need to mentally think of words to describe feelings, needs, or whatever. Speaking/praying/worshiping in tongues cuts out the natural mind in order for the spirit to commune with God directly.
It amuses me when I see people here complaining about the demonstrations they see of tongues on places like youtube, and say that it's just complete nonsense, no language at all. But the thing is, God is not listening to the words coming out of a person's mouth, it is the expression of the spirit that God understands.
For example, a baby may make unintelligible noises, but the mother knows what the baby wants, and whether it is just happy, or in need of something. The baby doesn't have a natural ability to express in a language what it is feeling or requiring. In the same way, a Christian may have a spiritual need, or express an inner joy,love, need etc, which cannot be expressed from their spirit using human words and wisdom.