Depends on how you buy it. If the phone is mail ordered, it would be possible to swap with a compromised device during shipping. NSA's Tailored Access Operations group is known to perform this sort of attack [1].

If you want to ensure you get a phone from the standard supply chain, buy it in-person at a store where you can see someone take it off the shelf.

http://arstechnica.com/tech-policy/2014/05/photos-of-an-nsa-...