First, you have to be corresponding regularly to justify asking these questions. If you are only writing one exchange per week or more, you are not in a serious correspondence, and therefore do not have the first commitment move. You know you have someone you can potentially meet in person if you are writing each other many times per week.
Once you are writing a lot, it should not be more than four weeks before you should be at least "talking about" meeting in person, if not actually making plans to meet. At this point also there should be interest to talk by phone. Meeting in person should actually happen between one and two months of the initial written contact. If the man does not mention the idea of meeting in person after four weeks of regular correspondence, then you should be considering cutting things off. Again, there are no absolutes, so you have to consider the individual, but it is very rare that a man who is interested in a woman will put off the next level of pursuing after so long. If he is not asking about speaking on the phone, then it might be time to end it.
Now, by "end it", I don't necessarily mean cut off correspondence. What I really mean is to start seriously engaging in correspondence with other men and meeting them (which you should be doing anyway). Many times women allow themselves to believe that because they are involved in heavy written exchange with a man online that he is very interested in her, and she feels she should focus on just him. That's a bad idea! Again, women MUST look for commitment moves from men before they start to consider stepping back from others. If a woman senses a man is serious about pursuing her, she will wait for him. Men who hold back showing any signs of commitment (even the commitment to meet) might not be serious about making the commitment to marriage. So men have to step up and take risks and ACT!! This is the sign a woman needs to stick around. Women who stick around anyway in the "hope" he will act are just setting themselves up for being hurt and wasting valuable time. Maybe he will come around eventually, but from my experience it rarely happens, and so many women have been hurt because the man never showed further interest. Then they wonder why the correspondence suddenly ended.
What if after several weeks of heavy correspondence he does not talk about speaking on the phone or meeting in person, but you really like him? This is tricky for a woman to do, but you should consider giving him a nudge by mentioning that you are open to talking by phone or meeting in person if he is. Men sometimes need just that little sign from a woman before they have confidence enough to take on a more firm leadership role. But after that first time, you should not do it again. Men are not attracted to women who continuously try to lead things along. It can be interpreted as being pushy or seeming desperate, etc. Give the man a nudge and then let it him take over.
If you don't get any serious interest from him as a result, then you should consider saying something like, "I have enjoyed corresponding with you and would like to get to know you more, but I am not open to just writing and believe that meeting in person is the best way to get to know if something more serious is possible to develop with someone."
A wise man will take this as a sign to step up, and a good man who doesn't want to lose the opportunity with a good woman will do the stepping up. A weak, indecisive man will fizzle away. And then you will have wasted only a month of your time and not many months, or years, for that matter. Some men will feel rejected by this. But that would be a foolish response, because a note like that clearly indicates you are interested and want a commitment move, otherwise you can't waste your time. I say this because I also know that many women are nervous to make this kind of statement out of concern that the man will be scared off and correspondence will stop (which is not a good feeling). But please be assured, a good man will be refreshed to hear this kind of thing from a woman and his respect level will increase.