I know this thread is a bit dated but.... I know quite a bit about this subject.
The software needed is here:
https://dedected.org/trac
DECT does include encryption, however in 98% of all cases the encryption either not used... or is used for only one side of the conversation.
In addition to that the Dect encryption is not very strong as is easily broken, in fact even GSM A5/1 has been cracked 100% at this time. (yes.. that is your cell phone) and I have personally confirmed this.
The hardware to intercept DECT as it stands today is quite expensive, only a USRP $1000+ or a modified driver for a DECT card made in germany (no longer in product, thus driving up the price) goes for around $500+ assuming you can even find one for sale... I hunted for months before buying my card.
However with things such as the RTL-SDR and the fact that dect is in the 1.9GHz range it is quite possible that some day we could use this device the only issue really being developing the software and finding the dongles that support that range (as some only do up to 1.7ghz)