Unsubscribe from iPhone app subscriptions ANYTIME and WITHOUT losing the rest of your trial/period

Unsubscribe from iPhone app subscriptions ANYTIME and WITHOUT losing the rest of your trial/period.
Note this will only work for subscriptions initiated from within an app - this is because such signups are linked to your Apple ID so you can control then through the Iphone's settings. If unsure - watch and give it a try!