This attribute indicates the current call type. This attribute has one
of the following values:
analogSpeech: Analog speech calls.
digitalSpeech: Digital speech calls.
analogPrefSpeech: Analog preferred speech calls.
digitalPrefSpeech: Digital preferred speech calls.
asyncData: Asynchronous data service calls.
g3Fax: Group 3 fax calls.
rejected: Rejected calls.
stuIII: STU III calls.
notUsedYet: Bearer Channel has not been used in a call yet.