10:48 am
The SIM itself will last indefinitely. After a number of months (I don't know how many) 7-11 automatically reassigns the telephone number but if you call them they will assign a new one and activate the phone.
Note: I believe that even after you have activated a phone, after a number of months of no activity, 7-11 will discontinue your telephone number even though you have money in your account. I'm not sure if they charge you to reactivate it.
11:53 pm
I been told by CSR that if you don't use sim card for 3 months, it will be diactatived. Just make any call out like *777 and counts as activity I believe. I think that 7-eleven has no idea when a phone is bought with certain number, so it will last indefinitly until activation. I also been told by CSR that they will replace a sim for $25, pending if you still have the damage sim.