I've noticed that google app engine seems to have a fair amount of downtime where they place the datastore into read-only mode. Frequently this downtime is in the middle of the day. Is this something that is happening only during early development, or is this something that I can expect to be always be occurring?

I've developing an application that helps small businesses handle their operations. One thing that it does is take appointments, another is route phone calls. I'd like some suggestions on how to handle times when the datastore is in read-only such as:

• What if our client is on the phone with the customer and is taking down an appointment and the datastore is in read-only? It would not be acceptable to ask the client to come back later to save, especially if its in the middle of the day.
• What if there is an incoming call and the application can not store the record or properly route the call due to database writes being unavailable?

How are these types of issues normally handled?