Nokia currently divides its cellphone offerings into one of three series. You have the Eseries devices that are devised for the business user, the Nseries which is where the top-of-the-line, multimedia rich handsets reside, and the four digit models which don't exactly fit into the other two designations. The manufacturer has just requested a trademark in Finland for use of the phrase Cseries. It is not certain that such a line will end up branded on products for the public and it isn't known what characteristics a handset will have to be considered Cseries. In this case, the best thing to do is to wait for an official announcement from Nokia, which could come at Nokia World 2009 in early September.
source: Puhelinvertailu (Translated)