Yellow color is the winner in all 5 colors of low-cost iPhone versions. Unlocked yellow iPhone 5C 16GB version is the first one that sold out. Its shipment date is also moved forward. If you want to buy an iPhone 5C with carrier SIM, you will get it by 9/20. But if you want to buy a SIM-Free version of iPhone 5C that comes with a GSM compatible SIM, you have to wait for 5 more days. As unlocked iPhone 5C will be shipped by September 25th.
Apple website reveals this fact that T-Mobile and others will ship the yellow iPhone 5C without contract but with varrier SIM on Septmber 20th. But T-Mobile will ship same yellow iPhone 5C with GSM SIM on Septmber 25th. 9to5Mac reports that this change of date is listed for only 16GB version of iPhone 5C. All the other versions and colors of the device are still listed to come by announced date of 9/20. Hong Kong and Canada will get iPhone 5C all models and colors in between 9/20 to 9/24 as Apple websites in these countries still mention shipment 'in 1-2 weeks' time.