The USA has never needed a search warrant to conduct foreign intelligence. A search warrant requirement is a 4th amendment protection afforded to US citizens. Foreign intelligence does not require courts unless you're trying to get foreign information from US companies (like the PRISM program and the FISA courts).

The FBI (who is responsible for all intelligence conducted in the USA, against foreigners or Americans) is absolutely required to get a search warrant.

The iPhone is one of the most popular phones in the world. Is it that crazy that the CIA is interested in them for intelligence gathering purposes?