New answers tagged sim
You should be able to just call up your network carrier and they can unlock it. I had the same thing. Just be prepared to wait couple weeks as the carriers say it takes up to 3 weeks to unlock. Or you can use a third party site like http://unlockingofficial.com I used this site couple times and worked great. It still takes a few days to get unlock though.
First of all, congratulations on buying your first iPhone. :) They truly are the best phones. Now, about your post: There's nothing bad about buying a used iPhone, as long as it's not iCloud locked. I've done it many times; the iPhone 6s I'm typing this on is the only iPhone I've ever bought new. The seller was right in not selling you the SIM card with ...
Go to a shop selling Sprint contracts/SIMs and buy one.
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