Obviously
It should be impossible for this to happen - and yet it should be possible to run any application on the iPhone like on a real computer. Just as regular computers should be safe from dialer malware.
It's really quite simple. One computer runs applications. A separate CPU handles telephony. So, with a computer with a dial-up modem - whenever you want to connect to a BBS or dial-up Internet, you have to dial the number on a separate telephone keypad that plugs into your modem - it cannot be commanded to dial out by the computer or software.
With a device like the iPhone, but more versatile, you have one physical button to switch from computer mode to phone mode - in phone mode, you're talking to a cell phone with a built-in browser and its own plug-in application format, protected by encryption; when not on the phone, you can be in computer mode, and play games and even write your own programs. In that scenario, the "phone mode" can be more locked down than the iPhone without limiting the versatility of the device, and the "computer mode" can be wide open, because the computer CPU has no access to the telephony capabilities.
Is this rocket science or what?