score:1
Yes, always declare. If you get caught with it and you don't declare it, you'll be marked as a "smuggler" and that will stay on your file for years. Every time you travel, they'll see that and you'll be more likely to be stopped. It happened to a few people I know. Also, if you want to apply for Nexus or Global Entry, you'll probably be denied.
Upvote:6
Yes, you have to declare it. Here is the form. There is no ambiguity ("including gifts for someone else" or "will remain in the U.S." covers either situation of you being resident or not).
I'm not a customs broker (so E&OE), but the harmonized tariff code for iPhones appears to be 8517.12.0050, which would appear to be free of duty. Your friend may be liable to pay use tax to his U.S. state of residence, but individuals often fail to do that, unless it's for business use.