Hello and welcome to PD / Bluelight
25I is most often the abbreviation for 25I-NBOMe, but like Infinite says, there is also the similar compound 25I-NBOH (and even more related chems starting with 25I). Yes they are analogues of 2C-I, but there are important differences, these NBOMe compounds are a lot more potent and can be much more dangerous as well. They also need to be taken in a different way, and the effects are also kind of different than those of 2C-I.
Don't want to alarm you unduly, but you might want to read the more extensive warning at the start of this thread:
http://www.bluelight.org/vb/threads...Me-drugs-where-did-you-first-learn-about-them
It is probably best if we write an NBOMe FAQ soon, but honestly it is wise if you do extensive research on these compounds before proceeding in any way.
Very simply put, NBOMe compounds like 25I-NBOMe have the potential to be extremely visual, "trippy", and also confusing sometimes making a person temporarily lose his marbles. However on the other hand many find them to be relatively hollow, lacking the "wisdom" drugs like LSD or mushrooms have intrinsically. Nevertheless it can be overwhelming mentally and physically and it is possible to overdose.
Be sure to read plenty of trip reports on Erowid:
http://www.erowid.org/chemicals/2ci_nbome/2ci_nbome.shtml (main page)
http://www.erowid.org/experiences/subs/exp_25INBOMe.shtml (trip reports)