am less than 3 days old on this site and am just loving it. I browse with my phone a lot as that is easier to access the net from where i come from. I use sony ericsson k800i and sometimes find little difficulties. I had to comment on someone's submission and could not post as I was told -167 characters remaining. I know it was wrong but i had to post in the YOUR ANSWER box and that went through. I will like to know what if its the same on pc and if there are other limitations when using the mobile version. Once again, am happy to be part of this.
Please don't use the answer box for comments. Answers are supposed to answer the original question, not to be used to reply to other answers. Answers that should be comments usually end up getting flagged by users and either deleted or converted to a comment by a moderator.
Also, avoid lengthy discussions in comments. They are meant for asking for clarifications and pointing out errors. If you find yourself going over the limit, that's usually a good sign that you should take the discussion to a chat room instead.
As wax_eagle noted, the character limit is 600, no matter what platform you use. Only how well that limit is presented varies by platform.
Let me suggest, however, that of you are hitting that limit, you are using the system wrong. SE differs from much of the rest of the internet in that it is not a social network OR a discussion forum. Back and forth engagement of ideas is discouraged in favor of clear concise questions and their corresponding answers. The comment mechanism is provided as a small feedback mechanism to improve the quality of posts, specifically not add a full on way to engage in a discussion of an issue like a comment form on a blog might.
If you find yourself wanting to do that, please consider that you are using the wrong tool for the job. Some of our community can be found in the site chat rooms where you can engage at length, but please reserve the QnA part for clear answerable questions and concise accurate answers and the comment space for furthering those goals, not detracting from them by turning posts into discussion threads.