Talk time is any time you spend on a call. Battery times are network dependent and will be reduced in poor network coverage areas. Standby refers to when the phone is turned on, but not being used to make or receive calls. When the phone is in standby mode, it uses minimal power to stay connected to the network. Standby times are affected by numerous external influences including the actual network, the reception level, whether the phone is in the one place, how much time is spent talking on the phone.
Batteries reaching the end of their useable life can affect both standby and Talk time.
Talktime refers to when the phone is being used to make or receive calls. Simplistically, whenever the person is talking on or listening to someone on the phone. Actual talk and standby times experienced on your phone in every day operation are network dependent and will vary significantly depending on your location. For example, if you use the phone in a weak or fluctuating signal area, the phone will be operating on maximum power and will produce a shorter talk time than if you are in a consistently strong signal area. This is done during standby and will occur more frequently if the phone is in a weak signal area.