Update: Mattress delivery was successful!
They actually do call, leave msg, follow up plenty of times 24hrs prior to the delivery. One time, absolutely no one picked up the store's phone, 2 other times, the gentleman who picked up the phone didn't sound all that professional.
Whatever, mattress was delivered when they said it would be, so no real complaint. Do watch out when they try to sell you a $80 mattress cover tho!