I'm the original poster. I misspoke in the original comment (too late to edit it). Now that I think about it, I believe unlocking does work regardless of cell

I'm the original poster. I misspoke in the original comment (too late to edit it). Now that I think about it, I believe unlocking does work regardless of cell service (as long as you don't extend the reservation, and try to unlock it after the original reservation time ends). I had the car towed twice: 1) First time, the car wouldn't start because the battery was dead while parked underground with no cell service. 2) Second time, the reservation was about to expire while parked without cell service, and I extended it on the app, but the car couldn't know that since the cellular unit couldn't phone home. EDIT: For what it's worth, I don't blame Zipcar for banning an unprofitable customer. I acknowledge that i was definitely pushing my luck by parking there a 2nd time after the first incident.