Could this meaning anything other than lesbianism? For example, if one considers the "natural use" of women to bear and raise children, perhaps not doing so (by choice or biology) would be considered "against nature"?
personally, i think paul means that they were holding positions in society contrary to paul's ideology. he indicates in other letter that he thinks women should shut up, stay at home, and do dishes.
the whole passage does not talk about homosexuality, it seems to be listing grievances: devil worship, women out of their place, and men screwing each other.