There are typically two phone-minute charging models: "Calling party pays" (Eurozone, others) and "Both sides pay" (US, Australia(?)).
In a "both sides pay" scenario, each customer pays for their own side of a call. I call your mobile from my mobile, we're each charged a minute per minute.
In a "calling party pays" scenario, the person who calls pays for both sides of the call. You can tell when this is happening by whether there are different rates for calling landlines vs. mobile phones.
The important thing here is what this means for pre-paid services.
In a "calling party pays" situation, a mobile subscriber can continue to make money for the telco _just by leaving their phone turned on_, regardless of whether they can make outbound calls. The inbound caller will still be giving money to the pre-paid caller's telco.
With "both sides pay", the telco of the pre-paid customer receives all revenue up-front; there's no subsequent money to be made because all charges come out of the credit balance of the pre-paid customer. Between that, and revenue recognition rules, it makes sense to expire that credit every 1-2 months because there's no other way to get a revenue stream off that customer.
There are typically two phone-minute charging models: "Calling party pays" (Eurozone, others) and "Both sides pay" (US, Australia(?)).
In a "both sides pay" scenario, each customer pays for their own side of a call. I call your mobile from my mobile, we're each charged a minute per minute.
In a "calling party pays" scenario, the person who calls pays for both sides of the call. You can tell when this is happening by whether there are different rates for calling landlines vs. mobile phones.
The important thing here is what this means for pre-paid services.
In a "calling party pays" situation, a mobile subscriber can continue to make money for the telco _just by leaving their phone turned on_, regardless of whether they can make outbound calls. The inbound caller will still be giving money to the pre-paid caller's telco.
With "both sides pay", the telco of the pre-paid customer receives all revenue up-front; there's no subsequent money to be made because all charges come out of the credit balance of the pre-paid customer. Between that, and revenue recognition rules, it makes sense to expire that credit every 1-2 months because there's no other way to get a revenue stream off that customer.