Send tones on every of this's contents which have the
IFACE_CALL_CONTENT_INTERFACE_DTMF interface.
For more details, see send_tones_async.
| this | |
| tones |
a string representation of one or more DTMF events. |
| cancellable |
optional Cancellable object, |
| callback |
a callback to call when the operation finishes |
| user_data |
data to pass to |