send
Sends DTMF events to the remote party. Valid DTMF events are 0-9, *, #, a-d, and A-D.
Since
0.1
Parameters
dtmf
any combination of valid DTMF events matching regex mattern "^0-9#\*abcdABCD+$"
callback
A closure to be executed when completed, with error if the invocation is illegal or failed, otherwise nil.