How to know where and when my iphone was bought?
I don't know of a public tool for looking this up. However, if you befriend an Apple Genius, I know that the system they use for creating tickets allows them to view the purchase date and sales channel it was purchased through. However, there is no way to tell direct location (i.e. Best Buy on Main Street in St. Paul), only the channel (i.e. Best Buy).

You can also deduce the purchase date yourself by going to Apple's Check Your Service and Support Coverage page. If you locate the expiration date for repair coverage, subtract a year from that to identify original purchase date. If AppleCare was purchased, subtract an extra year.