Let me first talk about my phone setup.
1. I use google voice + Obihai 110 (highly recommend) as a free land-line, google voice will forward calls to both my cellphone and panasonic 7644M.
2. I have one cellphone paired directly with 7644M with link-to-cell.
3. Finally, I use link-to-cell to pair my computer with 7644M, so as to make computer calls with skype, etc.
Below are the results for this setup, I numbered them corresponding to the above 3 different ways of using the phone.
1. There is no problem using GV this way, I read from one previous review that if GV forwards calls to both a landline and a mobile-phone, there will be a glitch that the other side cannot hear your voice. But in my case, GV forwards calls to google chat (which is converted by ohihai 110 to voip signal), and mobile phone. And there isn't any glitch at all. When receiving a call, usually 7644M would ring first, then after 2-3 seconds, my cellphone rings, I can pick-up either phone to answer the call.
2. Basic feature of link-to-cell phones, works like a charm, really easy to setup. One thing worth mentioning is its ability to transfer contacts from mobile phone to landline. However, to copy all contacts together as a whole to 7644M, your phone need to support PBAP (phone book access profile), which seems not existing in my cellphone. So I have to transfer contacts individually. Another good thing is you can make multiple calls using different handset at the same time. For example, if one handset is making calls using cellphone signal, another handset can still use the land-line to call someone else. I believe there can be 3 simultaneous calls (1 land line, 2 link-to-cell) at maximum.
3. This is like using it as a bluetooth headset paired to computer. The manual doesn't mention anything about it, but it turns out working well. Here are the steps to achieve this. First, use link-to-cell to pair the phone with your computer. After pairing is successful, your computer will automatically install the drivers for this blue-tooth handset. Then in the sound and recording devices, you should be able to see one new device named blue-tooth hands free audio. Now, if you want to chat on skype with this handset, dial a random number (I dialed 1) using the handset via the computer link-to-cell, since this is an empty number, you will not be connected to anyone. But after a few beeps, the handset will establish a voice connection to your computer. You can now chat via skype or any other chatting software with your handset, assuming you have properly setup the sound devices within these softwares.
One major problem using it with skype is that the handset would hang up either when skype finishes a call or when there is no call and no sound from computer for like 10 seconds. This means after you dialing 1 with the handset, you need to dial the person you need to call immediately on computer, and the connection only last one call, after which you need to repeat again to establish connection. The numberpad on handset works with some lag in skype. I guess there is some workaround for skype to maintain a constant or automatic connection, but didn't figure out how.
I also tried to set my default audio device as 7644 on computer, and played mp3 via the handset speakerphone. It's mono sound obviously, but acceptable for some audio books. I tested for about 10 mins without seeing any problem, and handset automatically hang up after I stopped music for 15-20 seconds.
As you can see, this phone integrates all of my phone services. Whenever I receive calls from cellphone, GV, skype, I can answer them with it. I can also make calls with it using all the above services.
A few comments for the difference between 7641 series and 7621 series if someone wonders. They are basically the same except for
1. handset on 7641 have headphone jacks.
2. You can dial and speak via the base unit with 7641, while 7621 only have the answering machine function on the base unit.
3. For the same reason, 7621 doesn't have base unit display, and there is no intercom between base unit and handset.
4. 7641 have power back-up mode during power failure, which means you can still make calls even there is a power outage less than 13 hours.
5. I didn't see on 7621 description page it has range-boost, while 7641 clearly says it has range-boost, which allow 20% more distance between base unit and handset.
So if you only use your handset to make calls, and your area doesn't have power outage once in a year. Then probably 7621 could also meet your needs.
I just played with it for half a day, so cannot comment on its reliability. But for its versatility and good sound quality, I would vote it for more than 5 stars!
a few small glitches of the phone.
1. Bluetooth headset: This phone system supports connecting to a bluetooth headset, as one would usually do with a regular cellphone. The headset function works, but probably not in conjunction with link-to-cell. However, my problem is, after the headset is registered with the phone system, it cannot be removed, and this causes problem if you want to connect the bluetooth headset to another device, like cellphone or computer. Suppose I paired my BT headset to my cellphone, if someone rings me and I want to pickup the call by pressing the button on the BT headset. Right now, every time I tried to do this, the BT headset will connect to panasonic phone rather than my cellphone. It's not a big issue, but annoying sometimes.
2. Voicemail notice: The phone has built-in voicemail. But as others mentioned in the comment, after receiving the first voice mail, there would always be a "new voice mail" notice appearing in both the base and the headsets. Since I usually use GV voicemail, it's not a problem for me.