The ATS X10001P is a SIP basestation with a cordless DECT handset. While this phone is bundled with the Lingo service, it is quite easy to unbundle it. The key to reconfiguring the device is the root password, which is ‘test’. Once in, you can update the various configuration pages to use your own SIP server (such as Asterisk), instead of using the Lingo service.
These phones are available at Staples.com. You can obtain the crack (plus more notes) from Asterisk.DrunkCoder.com