Can I block entire area codes from my iPhone?
Yes, there IS a free and easy way to block incoming nuisance calls on an iPhone!

(1) Get and install a silent ringtone (I use one called "10 seconds of silence" which I found on the internet for free).
(2) You know who your regular callers are. Give each contact a ringtone other than the default. (Yes, it takes a few minutes, but it's a one-time thing.)
(3) Set your phone's default ringtone to "10 seconds of silence".

From then on known callers get cause your phone to ring with whatever ringtone you've assigned that particular caller.

Calls from unknown callers will not cause your phone to ring. These callers can leave a message if they wish. Most spammers don't bother.

Repeat nuisance callers can have their numbers added to a special "Spammers" contact which you can block so that such callers cannot even leave messages. Just remember that if you do this, you have to unblock and re-block this contact each time you add a number. Don't worry about whether you indicate the number is fax or mobile or whatever--doesn't matter. I used to do this last step, but found it was unnecessary. Plus I kind of like to look once or twice a day and see where the spammers are ostensibly calling from--of course, their really using spoofed numbers using VoIP over the internet.