Well, I wouldn't consult an attorney; this isn't a legal matter. An attorney's opinion on this is worth no more - and possibly less - than anyone else (worth less because an attorney doesn't have any personal experience with the sort of work setting you're in).
Start by considering this from your manager's viewpoint: you've been working there in your permanent position for two (three?) months, and you already want a pay increase?
Another thing to consider: annual reviews are a good time to discuss salary, but there are other good times as well - after someone has very successfully completed a major project, for example, or when there is a significant change in job responsibilities. Don't make any assumptions about annual reviews being a major timing factor.
So, specific advice: Wait until you're worked at least six months in the job (starting from the date of hiring into the permanent position), then evaluate whether you've done really good work. If so, go to your boss and say that you understand why you were hired at significantly less than the industry average - because the company was taking a chance on you. But now you think you've proven yourself, and you think a raise is in order to get you closer to the industry norm.
Be prepared to be told that (a) it's too soon for a raise, either because of the manager's general approach to raises, or because of company policy as to timing of raises; or (b) that the manager wants to discuss this at your annual review. If so, the best decision is probably just to wait, keeping in mind that you've planted the seed for a significant raise. And keep doing good work.
Two other things to keep in mind:
First, while companies often do take advantage of new employees who don't recognize their own market value, you did voluntarily agree to the salary, and, if you hadn't found out about what others are paid, would have been happy with it. So no one at the company is likely to be apologetic about your current salary level, or feel that they "owe you" to raise it. By providing them with a solid six months (or year) of good work, you give them a reason/rationale for raising your salary.
Second, if you put in a solid year of good work, you should learn a fair amount, and then, if you're not given a pay raise you think is fair (this assumes you don't get a raise earlier), you have improved your skills and resume when you start looking for a new employer - an employer who might well give you less consideration if you'd worked for far less than a year at your current job before you started looking for a new job.