You’ve read this correctly — iPhone WILL support 3rd party apps. But don’t expect the full openness as Symbian, Windows Mobile or Palm OS have — all apps will rather pass through some Apple’s approval process.
In an interview with Walt Mossberg, Steve Jobs said: “This is an important tradeoff between security and openness. We want both. …we’ll find a way to let 3rd parties write apps and still preserve security on the iPhone. But until we find that way we can’t compromise the security of the phone. …I’ve used 3rd party apps… the more you add, the more your phone crashes. No one’s perfect, and we’d sure like our phone not to crash once a day. If you can just be a little more patient with us I think everyone can get what they want.” (via: engadget)