Asterisk is nothing but a Software implementation of Private Branch Exchange. Mark Spencer of Digium has wrote this application once he is not able to find a PBX for his company. Now this application is using by lot of people for medium , and large scale enterprises.
ISSUE
The signals from a DTMF system is not recognised by the Asterisk. Specifically key press from Smart phones and Mobile phones who is sending DTMF signals.
ASSUMPTION
You have a working Asterisk system
Add the following line in chan-dahdi.conf file
relaxdtmf=yes
toneduration=300
toneduration=300
Save and Exit.
Reload the Asterisk.
Now you will be able to receive the Signals from DTMF devices.