As many have previously described, this phone is NOT for the "techniphobe" or faint of heart. There is much programming and referencing the Owners Manual during the initial setup. You will also need to keep the Owners Manual handy, as there may be times that you want to change some settings. Unlike other less functional phones, this one does not have an easy to use menu system to select and deselect options. Instead you must enter specific codes, listed only in the manual, to change the options (i.e., programming the phone).
That said, this phone is feature rich. I have had other Panasonic phones in the past, including my last ones which were also DECT 6.0 (KX-TG9333), and this compares very well. I had to replace the previous set, as I am now working solely out of my home office, and needed a corded phone with speaker phone option so I would not be reliant on a battery powered handset that lasted only an hour or so per charge. (I was constantly on conference calls, using the speakerphone portion of the older handsets, and having to use two or three handsets to get through the day.) An added bonus of this phone was the ability to also pair a Bluetooth headset to the base, which also gives clarity (compared to the speakerphone) to the conference calls as well as cordless convenience. Once paired, switching from the Bluetooth headset and base unit is as easy as pressing a button on the base to use the speakerphone (or headset) or simply picking up the corded handset.
Calls sound as good as I would expect. The corded and cordless handsets are great. The speakerphone quality depends on how close the speaking person is to the phone (base or cordless handset), yet it is very good for the most part; I would not expect anything different in a phone kit in this price range. One thing to note about the base unit speakerphone: The mic is hidden on the underside of the base, just to the right of the speakerphone button (refer to #6 on page 12 of the owners manual); this area must not be blocked or else the mic will be useless. Not exactly the best location for the mic.
I am currently using this phone with Vonage as my VoIP provider. I get notified when there are messages awaiting to be heard in the Vonage phonemail on the base unit and cordless handset screens. Programming the Vonage phonemail access number was not difficult (it was more difficult finding the number in the first place, as I had forgotten what it was -- "*123"), so now I can access my mailbox with a single button press when there are messages.
I cannot talk to the pairing of cell phones to the base/handsets, as that function is not one I plan to use. But it does look interesting for some people.
Although Panasonic specifies using two (2) AAA NiMH batteries as optional in the base, I highly recommend using them, as they will be used during a power outage, giving the phone up to 7 hours of use (depending on power saving mode set). I also am unsure if the settings would be preserved during a prolonged power outage without the backup batteries.