apple care if purchased from another store?

If you can't buy it with the phone you can buy it within 60 days. See the information below from http://www.apple.com/support/products/iphone.htm

Important notes

Purchase AppleCare+ with your new iPhone. Or buy it within 60 days of your iPhone purchase:

• At an Apple Retail Store (inspection of iPhone and proof of purchase are required)
• OR call (800) 275-2273 (requires you to run a remote diagnostic and provide proof of purchase)

Yes.

Note that you may be able to buy AppleCare+ when you buy the phone. You can do it at AT&T for example: http://www.att.com/esupport/article.html#!/wireless/KM1045162

60 days to do if otherwise. Since Apple needs to run a diagnostic to determine the device is OK prior to AC+ purchase and activation, don't wait till the absolute last day.