This attribute, if set to a value of allowed indicates that outgoing
calls (from the DTE to the network) can be made using this
particular Dna. If set to a value of disallowed, then outgoing calls
cannot be made using this Dna - such calls will be cleared by the
local DCE. This attribute corresponds to the ITU-T 'Outgoing Calls
Barred' feature for Dnas in that outgoing calls are barred if this
attribute is set to a value of disallowed. Either outCalls, or incCalls
(or both) must be set to a value of allowed for this Dna to be
useable.