Some phones don't natively support DTMF. For example, disk phones created only for pulse dialing. If you have such a device, you can use its functions.
Almost all modern telephones there is a mode switch dial. It is normally moving the switch slider. Also, it is always present on the switch “Pulse/Tone”, which corresponds to the pulse and tone modes. Turn the switch to “Pulse”. So, your phone has replaced the mode dial.
If this switch your model of phone is absent, the same function of switching modes will perform the key " * " (asterisk), which is present on the numeric keypad of your mobile phone. Press again to return the phone to its previous mode dial.

Sometimes after the change of regime is required to lower the receiver and re-raise it. That is, during a call, move the machine from one mode to another is virtually impossible on some models of phones.
If you have a DECT phone (i.e. a phone that has a wireless radio receiver), the mode sets are in the setting of "base" to which the "tied" up. Access settings directly from the phone handset of the machine or the control buttons on the base.
Read the instructions for your handset. It will necessarily contain information about your machine setup, including the transfer to tone or pulse dialing mode. You can also find the user manual on the manufacturer's website or the websites created to help users.