{Edit:}
convert pulses from an old rotary phone into tones
The problem is that the OP said "Rotary Phone" that is a phone that when dialing shorts the handset and shorts the phone line in a 60/40 mark, space 10 PPS max rate (I could be off in the speed as it has been 30 years since I did this type of work). It isn't tone dialing unless the OP has mistaken his "nomenclature" and the DECT6 system is a digitally encoded audio and data stream between the base unit and the handset. So If you really wish to "Dial" from the handset you must emulate the dialing "Pad" or switch matrix to dial the number and IF it is automated calling what provisions do you have to detect dial tone so you can dial the number. There is also the condition where the phone number being called is busy or there exists a circuit busy condition. Both must be considered, first, I should think and you made no mention of any provisions for those conditions.
Doc