But the main point here is that in the first 6 months the retailer has to prove the fault was not present at the time of delivery. But after 6 months that proof moves to you and could involve getting engineers report and cost you.
These are provided in addition to the minimum requirements (soga) and lay down the length the Manufacturer covers the item (not the retailer). I will not delve too deeply into individual companies terms and what is covered but will link to them at the end. But a warranty from the manufacturer is for a set period. During this period you the consumer just returns the item for repair under the warranty directly to the manufacturer I.E. you do not have to prove faulty on delivery (unlike soga after 6 months).
Some Manufacturers will allow you to purchase an additional cover for the phone to extend the time the manufacturer will treat the phone as though it was still in an original period of cover and again offer you cover that exceeded the soga requirements.
So in brief, if you have a faulty handset and want a good level of service to use the manufacturer's warranty as it offers the highest level of protection for the consumer.
Normally Accidental damage and water damage are excluded by soga and warranty but some extended warranties cover these incidents.
Links to some of the warranty's (some you need to read small print)