There is mentioning of other apostles in Acts & elsewhere in Paul's letters.  These seem to be people who either are major workers in the church, or leaders & evangelists, like Paul.  So yes Junia is probably a major player since Paul has referred to her as an apostle.  

Interesting what the JuniaProject brings up re: 1 Tim 2:12 and thanks for the link - I had not been on it before now.  However, what is most likely according to those who study St. Paul is that Paul never wrote 1st Timothy at all or the Letter to Titus.  To the experts on St. Paul, the writing is too different and I agree that it kind of turns on itself.  We have Paul who makes fun of the Galatians for being too concerned with the legality of everything they do, but who then writes 2 letters which only concentrate on making church structure in a very legalistic fashion.  Often people wrote letters & signed famous people's names to them hoping they would be more accepted and experts agree this was likely here.