"The best business telephones in the world."

We are looking into Text Messaging om the DECT M300/M700 to M25 and M80 handsets. 

The documentation vaguely states the base station uses a proprietary protocol, and a 3nd party server can be used.

Where can we find documentation on the proprietary protocol and are there any supported servers? A list would be nice.

and

Sending SIPSAK message "sipsak -i -M -B "Test message" -s sip:100@192.168.1.10" to the base station is accepted, but nothing shows up on the handset.

Thanks in advance.