About Talk time (battery life)
Talk time (battery life) is the formally quoted longest time that a battery charge will last when you are always talking on the phone based on a single charge.
The talk time is very reliant on the cell network condition, for example, the distance to the nearest GSM cell tower. Moving quick while talking (as in a vehicle) also has negative effect on battery life.
Frequently you will discover the Talk time field in the specification of new GSM phones empty because the manufacturers in some cases neglect to reveal the information at the time of the official release. Later on, when the phone hits the market, the figures are normally revealed.