"You can configure Cisco CallManager SIP devices (lines and trunks) to always use an MTP. If the configuration parameters are set to not use an MTP (default case), Cisco CallManager will attempt to dynamically allocate an MTP if the DTMF methods for the call are not compatible. For example, SCCP phones support only out-of-band DTMF, and Cisco SIP phones (model 7905, 7912, 7940, 7960) support RFC2833. Because the DTMF methods are not identical, Cisco CallManager will dynamically allocate an MTP. If, however, a SCCP phone that supports RFC2833 and out-of-band, such as Cisco IP Phone 7971, calls a Cisco SIP IP phone 7940, Cisco CallManager will not allocate an MTP because both phones support RFC2833. By having the same type of DTMF method supported on each phone, no need for an MTP exists."