I got my iPhone 6 from Future Shop (in Canada). A month or so later I walked into an Apple store and purchased Applecare+. They sales guy just looked at my Serial #, typed it into his portable iPod touch, I paid via VISA and got email receipt - all took about 2 minutes. He didn't even want me to take out of case or examine it... just wanted serial number.
I got my phone from Verizon and went to a certified Apple repair store and they checked over my phone and sold me the warranty. The place was called Mac Pros which is a local certified store. You can do a search in your city. Choose Service.