I'm quite sure that the FBI has been throwing a lot of money and resources at this problem, and sooner or later it was on the cards that it would come up with an answer.
My own feeling is that a great deal of unnecessary fuss has been made by Apple over this issue. It seems to me that the company has deliberately set out to make a big thing out of what is - on the face of it - a straightforward issue. A lot of hysteria has been stirred up, and attempts have been made to portray the argument as a noble stand (by Apple) for the individual's right to privacy.
There is no threat to anyone's privacy that didn't already exist - if the FBI can break the iPhone's security then others could do it. Surely it would be far better for Apple to have said 'OK, we appreciate that this may be a matter of national security, so we'll do what has been asked of us, and we'll make sure the door is locked when we've finished'.
Known terrorists do not have a 'right' to conduct their atrocity planning behind an impregnable wall of security that is provided for them by giant software and hardware companies.