Except they either won't call back at all, or will call back way later than promised - usually when you decided it's not going to happen and moved on with your

Except they either won't call back at all, or will call back way later than promised - usually when you decided it's not going to happen and moved on with your day, and now you don't have any of the documents and data you need with you and actually are driving, so the callback is useless.