I bought the Panasonic KX-TH1212B system and 4 expansion handsets(total of 6) and really gave it a try. I wanted a system that would allow us to both get rid of our land line and still be able to use our landline type home phonesets - we could thus just live via a cell phone connection.
The Panasonic expansion phones and the link between phone and base works well, the bluetooth connection I found to be a nightmare. I tried three phones with bluetooth, a new Apple IPhone, a 8310 Blackberry curve and a Motorolla V557. None of the phones will drive the Panasonic connection. I got tired of coming home and getting little love notes and frowns from everybody in the house regarding our new phone system and it's poor performance.
In comes the solution: I went out and found a Siemens Gigaset One. This system has worked very well for a month now. The Bluetooth connection has been flawless with all three phones listed above. I get a little static on the line at times, but worth the $50 a month we save.
I now use the Panasonic system I bought as the home handsets via a cable from the Gigaset One - a use at which the KX-TH1212B works well. I used a line splitter to also drive another older Panasonic home system with 4 cordless expansion handsets. We have an extension phone everywhere!
If you want a system to connect to your cell phone via bluetooth and dump your landline, buy the Siemens Gigaset One and then any old home cordless system will work very well!
Dave in Oregon