iPhone OS 4.0 has made the iPhone more secure for business users.  Instead of the simple 4 number passcode lock, you can now create a more secure password using the entire keyboard and all the characters.  This is a very nice feature because 4 number passcodes can easily be cracked.

It seems that you can make this password as long as you want.  I know that this feature alone was holding back certain companies from letting their employees use iPhones.