If you think about it, this physical access requirement severely limits the threat of cell phone spying. An anonymous criminal tapping into your phone from across the Internet is frightening; having a family member or ex-boyfriend spy on your phone is still spooky, but that's not really a technology problem. After all, someone who had possession of your phone long enough install software could also read through your sent text messages.

There have been some demonstrations of spyware being added to cell phones without physical access -- over short distances using Bluetooth technology, for example.
http://redtape.msnbc.com/2007/06/just-how-easy-i.html