Stockpiling more than a week's worth of any supplies is, for most folks, just plain foolish. I have heard conflicting stories that cell phones and satellite phones still use land-based switches. The US phone system is in good shape. If there are going to be problems, it will be with billing. Switches operate without regard to the date, they deal with connecting circuits in milliseconds.
Cellular networks are much better off, because they are much more recent.
Yes, there's a possibility. No, absolutely not. The FDIC insures the money while it's in the bank. Leave it there. Yes, they could.