Hi.
"Both the CrmService Web service and the MetadataService Web service contain messages that will work when offline. You can find out if a CrmService message works offline by retrieving the information for the message from the sdkmessage.availability property. This information is shown in the list of CrmService messages. For the metadata service, only the retrieve methods are available offline. This information is shown in the list of MetadataService messages."
Cheers,
Adi