Sems that i’ve been right with my ideas how Apple is going to open up the iPhone (see here and here). Ive just read on AppleInsider that Steve Jobs announced that there will be an SDK by February.

In the announcement there is a direct reference to the security through digital signaturs concepts i anticipated they will use (as Symbian and J2ME are already doing):

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.