I don't know if that's true, but if I had the same power as a government agency, which would allow way higher salaries than Apple's or any other hi tech corporation, that's the first thing I'd attempt to do: find ex/unhappy/disgruntled engineers and offer them 5x pay plus a luxury home and lab in some tropical island.
Also don't forget the hardware. Like with most/all other phone vendors, iPhone chips aren't made in the US; most of the design maybe is, but the chips themselves are not, and finding a Chinese hardware engineer happy to help would be even easier because all he should implement is a covert channel to tunnel sensitive data (passwords?) to a known place. If you have access to the hardware that should be trivial to do: just implement a small undocumented flash memory space anywhere, then when the user taps a password an also undocumented firmware routine (that's hundreds of bytes, very easy to conceal) would add the password in that small memory that can be read only in certain conditions (say connecting power+tapping a bossa rhythm while with the phone screen is facing down+disconnecting power - that seems crazy but you get the idea: every sensor is a switch and any switch can be used to enter a code). A few spare kilobytes of memory here and there would allow this and other spying mechanisms, so I would't be surprised at all if some big agency would attack the hardware/firmware rather than the software.