clicknz: Hi - yes, I would certainly suggest that you get something in writing with regard to the replacement. I believe the usual practice is to still only give 12 mths warranty from the original purchase date rather than starting again with the date of receiving the 'new' phone (this may possibly be a refurbished unit).
Either way, anyone with Apple hardware can check the status of their gear by keying in the serial number at this site https://selfsolve.apple.com/agreementWarrantyDynamic.do
Yes that is true, you usually don't get 12 new months of warranty for that switched item. But you are still covered by the CGA if you pruchased it for personal use.