you can log in from everywhere at any of the sites you wish to. Moves are made, no matter where you made them. 🙂
Read the (short) answer to the question "Why do redhotpawn.com, chessatwork.com, redhotchess.com and timeforchess.com exist?" at http://www.redhotpawn.com/help/index.php?help=faq (2nd last)
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