Apple has posted this letter to the community on the Apple.com web site at:
http://www.apple.com/hotnews/

Third Party Applications on the iPhone

Let me just say it: We want native third party applications on the iPhone,
and we plan to have an SDK in developers’ hands in February. We are excited
about creating a vibrant third party developer community around the iPhone
and enabling hundreds of new applications for our users. With our
revolutionary multi-touch interface, powerful hardware and advanced
software architecture, we believe we have created the best mobile platform
ever for developers.

It will take until February to release an SDK because we’re trying to do
two diametrically opposed things at once–provide an advanced and open
platform to developers while at the same time protect iPhone users from
viruses, malware, privacy attacks, etc. This is no easy task. Some claim
that viruses and malware are not a problem on mobile phones — this is
simply not true. There have been serious viruses on other mobile phones
already, including some that silently spread from phone to phone over the
cell network. As our phones become more powerful, these malicious programs
will become more dangerous. And since the iPhone is the most advanced phone
ever, it will be a highly visible target.

Some companies are already taking action. Nokia, for example, is not
allowing any applications to be loaded onto some of their newest phones
unless they have a digital signature that can be traced back to a known
developer. While this makes such a phone less than “totally open,” we
believe it is a step in the right direction. We are working on an advanced
system which will offer developers broad access to natively program the
iPhone’s amazing software platform while at the same time protecting users
from malicious programs.

We think a few months of patience now will be rewarded by many years of
great third party applications running on safe and reliable iPhones.

Steve

P.S.: The SDK will also allow developers to create applications for iPod
touch. [Oct 17, 2007]