In England,
Irene was originally pronounced eye-REEN-ee, which is truer to the original Greek form. If you've ever watched the BBC version of "The Forsyte Saga" that pronunciation is used. I love the name as eye-REEN-ee. (That is the pronuncation of
Eirene as well).
Oxford says: It was formerly pronounced in three syllables, as in Greek, but is now throroughly naturalized as an English name and usually pronounced as two syllables.