Could asterisk SIP extension be configured as a modem like extension to able to auto answer call, read DTFM digits, and send special tone? Any equipment need to be purchased to do that?
Thanks
No. Such extensions would have no technology driver associated with them so they would just be Asterisk extensions (SIP extensions is really a FreePBX concept).
No.
You can probably do what you want to do, but there is no SIP involved downstream of the extension.
Note that accurate transmission of tones means you cannot use low bit rate codecs. SIP has special treatment of DTMF, but not of other tones.