Engadget says that's the box for the white iPhone 4 shipping to Vodaphone retail outlets in the UK. Someone unwitting sales associate sold one to a customer before Vodaphone sent out a comapny-wide email halting sales until "next week."
There's also a shot of the phone itself here, which offers up another piece of legit evidence this thing is coming sooner than later (the exact date is still uncertain). But it does line up with 9to5mac's claims that the white iPhone 4 will start selling on April 27 (next Tuesday). [Engadget]