Asterisk SIP phones can't detect inband DTMF!?

Can anyone out there prove or disprove that assertion?
Has anyone successfully created a SIP phone that detects DTMF tones within a wave form received? I haven’t. I’ve tried with no success.

I could certainly use an successful example,
Most helpful would be the associated sip.conf file, extensions.conf file, and Originate command.
Any other configuration requirements outside of these would be very useful. I’m very concerned that there are some other settings which I’ve omitted that preclude the inband DTMF recognition and conversion to “DTMF” events which I can process.

I’m expecting(hoping?) to receive the same events I do see when I have phones send out-of-band RFC.
Example (parsed for display):
150303-091144.16604 Event: DTMF
End => ‘Yes’,
Event => ‘DTMF’,
Uniqueid => 1425391875.2,
Privilege => ‘dtmf,all’,
Direction => ‘Received’,
Channel => ‘SIP/’,
Digit => 2,
Begin => ‘No’

If possible. but not necessary, a “-d” logger trace with “sip set debug on” would be very useful.

Many thanks for you attention and assistance.