Nimnim
The Nim
They can't fire you for a single no call, at most they can give you a warning letter. If you called in properly, my supplement says 1 hour before scheduled start time, then you can either bring in your phone, which may require a property pass to get back out, or you get your phone bill which states the numbers called at what time.
As others have said it's a good idea to have a sups number to call them. I'm surprised the main call in number you have doesn't have voicemail, but that just means if they don't pick up they don't know, as long as you're not calling way too early for your shift.
As others have said it's a good idea to have a sups number to call them. I'm surprised the main call in number you have doesn't have voicemail, but that just means if they don't pick up they don't know, as long as you're not calling way too early for your shift.