This was really helpful, but didn't answer my question. It should clarify things for you:
If you don’t use your cell for two months, your minutes disappear.
If you have lost your minutes after not using the phone for two months, but purchase more minutes before four months from your last phone call, you recoup your lost minutes.
If you don’t use your cell phone for four months, you lose your minutes permanently.
If you don’t use your phone for six months, you lose your minutes AND your telephone number becomes inactive. You must buy a new SIM card and reregister your phone. So even if you keep your phone for emergencies only, make a call or send a text once in a while to keep the phone active.