Same here. Large increase in spam traffic to my iPhone 5 today. Disturbing.
Given Apple's size and growth rate, I'd definitely recommend protecting the
client-base by implementing strong filtering.
I am shocked there is no existing filter mechanism in place that caught these.
But don't switch to others just yet. Give Apple time to fix the error. Code is probably
being written right now to deal with the issue.
Thinking about my earlier proposal in this thread, the filtering is probably done on
the SMTP and IMAP servers in the cloud, rather than at the client (iPhone, iPad, etc.)
And, what I'd suggest, is add a secondary filter mechanism to an rushed-released version of
the iDevice Mail app, with choices similar to what appear on the Mac OS X
Mail app (always from contact book) but also include whitelist/blacklist ideas,
Bayesian distribution spam-filtering, and so forth, or simplify it so it isn't too confusing.
Concentric rings of security are important and spam is a very significant issue generally
which annoys customers and causes market share drop.
The above is how I'd handle it if I was coding it. If I've missed something, please let me know.