iPhone 5C and 5S appeared on the Straight Talk Activate Your Service page. New phones usually appear on the Straight Talk activate phone page a few weeks before they are released. But sometimes phones languish on that page for months only to disappear without ever being released.
Update: Straight Talk representatives on Facebook are saying that iPhone 5S and 5C will go on sale tomorrow 12/6/2013 and that the phone will run on a GSM network and will have 4G data of some kind.
It looks like the GSM opperator may be AT&T. A user asked "Those iPhones 5c and 5S are GSM or CDMA , i mean are they gonna work of AT&T or Verizon towers ?" and Straight Talk replied "Hi! The new branded iPhone phones are under a GSM tower which you have mentioned."