Not to bad. Link to the description of the phone.
Nevertheless I am working on a 65 gram bird tracker with the target to run endless. Right now Eneloop batteries are in use. Eneloop offers a self-discharge of 25% within 3 years. If the self-discharge is linear, then after 15 years 23,7 % capacity is left. Such a AA cell offers 2400 mAh hours. After 15 years will be still 577 mAh left.
The phone promise 10 hours talk time. 10 hours talk are 5 hours transmit and 5 hours receive? I am not sure. Anyhow a state of the art GSM module discharge the battery with 230 mA during maximum power level of 2 Watt. 2400 mAh / 230 mA = 10,41 hours. So after charge the 10 hours are possible and after 15 years we have 577 mAh / 230 mA = 2,5 hours transmitting time left.
The AA batteries are public at the link as below. Just calculate yourself.
Anyhow, this phone could run endless too. It just has to use energy harvesting by solar or temperature delta.