The advantage of flip/slide mobiles that increase their length when used - is that the sensitive bits are protected when not in use.
My home cordless has a pad button lock feature by holding * for few seconds. Pressing * twice will unlock it.
For convenience you can receive a call when the pad is locked. The other day the caller was a utility company wanting my meter reading - and offered me several "press button" options. I then discovered that the unlock feature doesn't work while a received call is in progress.