"Speaking in tongues" is not only a Christian phenomenon. Regardless of whether or not the "gift" is for today, one still cannot point at speaking in tongues as "proof" that they are baptized in the Holy Spirit.
History of the Church 1:295-297, November 1832: "About the 8th of November I received a visit from Elders Joseph Young, Brigham Young, and Heber C. Kimball of Mendon, Monroe county, New York. They spent four or five days at Kirtland, during which we had many interesting moments. At one of our interviews, Brother Brigham Young and John P. Greene spoke in tongues, which was the first time I had heard this gift among the brethren; others also spoke, and I [Joseph Smith] received the gift myself."
While Mormons share our Scriptures (while translating and interpreting them differently) and are (in their own sense) followers of Christ (although not a Christ who is in full equality and deity with the Father), are not "saved", in the way we are.
The Oracle at Delphi needed interpreters to pass along her "wisdom". There is speculation as to whether or not the wisdom was "tongues" or "riddles" that needed interpreting. There does also seem to be some indication that the trance of the Oracle was due to some intoxicating substances that seeped out of the lower regions of the cave that she prophesied from.
This is not a wonderful example, but it does indicate that "ecstatic speech" was an indicator of the prophetic in religions other than Christianity - and before Christ walked on earth.
in 1956 Carlyle May wrote an article in "American Anthropologist", "A Survey of Glossolalia and Related Phenomena in Non-Christian Religion." I cannot get to the entire article, but the first page is here.
"Ecstatic vocalization in the form of incoherent sounds and foreign words has long been on interest to students of religion. (...)This paper will show that glossolalia and similar speech-phenomena occur in various forms during shamanistic rites of the New and especially of the Old World. (...)
Herodotus (Lombard 1910:90) speaks of an inspired priest in Greece who suddenly spoke in a barbarian language, and Virgil in the Aeneid (1953: vi. 44-49, 97-99) tells of a Cumaean sibyl who spoke strangely while possessed. The Old Testament (Lombard 1910:89) alludes to a form of ecstatic behavior similar to glossolalia. Guillaume (1938:144-45) states that in 853 B.C. four hundren prophets raved in ecstasy before the gate of Samaria, and in ancient Egypt (Erman 1894:352-55) necromancers uttered formulas, believed to be revelations from the gods, made up of foreign words and senseless noises. The more mysterious and incomprehensible these formulas were, the greater their power was thought to be.
What about xenoglossia?
- Swarnlatta Mishra: A girl in India who lived entirely among Hindi-speaking people but was able to sing songs in Bengali, as identified by Professor P. Pal of Itachuna College in West Bengal, who studied the case after Professor Stevenson and transcribed some of the songs.
- Uttara Huddar: Uttara was a woman in India who normally spoke Marathi but, after participating in a meditation during a hospitalization, began speaking in Bengali, much to the bewilderment of her parents.
- Two hypnotic regression cases: Professor Stevenson is quite skeptical of most hypnotic regression work but he did have two cases that included responsive xenoglossy; that is, hypnotic subjects who could converse with people speaking the foreign language, instead of merely being able to recite foreign words. One is that of Jensen, an American woman who, while under hypnosis conducted by her physician husband, described being a Swedish peasant farmer and was able to converse in Swedish. The other is Gretchen, an American woman who was hypnotized by her Methodist minister husband and began spontaneously speaking in German. She described the life of a teenaged girl in Germany, and Professor Stevenson, who is able to speak German, was able to converse with her. (from wiki...hopefully the links to the citations are there, the link to the page is here.
It seems clear that (whatever "tongues" is) and whether or not "tongues" is for today, that the phonomena is not limited to Christianity, or even to religion.
In "testing the spirits", we need to look at all the evidence and not blindly follow. It may very well be real (in some cases and in some cases not), but we need to look realistically.