A little bit of research (I downloaded the manual AND read it) on the Panasonic BlueTooth pairing, seems that while you can pair up to 2 cell phones, you can only have one connected at a time.
For me, that's a no-go. I would be faced with my wife telling all her friends/family (not really that many) to just call my cell phone. Then for every call she missed, I'd get the voice mail on my cell line that would need to be transferred. Or I could ignore and simply say "Why are they calling my cell phone", but thinking that's not going to go far.
All kinds of potential problems here.
EDIT: Nothing like the internet to do research. Here's a cheaper solution to Panasonic. Let's you pair and connect at the same time, up to 3 cellphones, with no need to replace the existing home telephones. $64 at Amazon.
@ Dnvr. Yes you can make it not ring at night. You simply turn off the cell phone. No cell phone, no BlueTooth pairing, no ring. Or you can turn off BlueTooth. Or if it's an iPhone with OS6, enable "Do Not Disturb", which only allows calls you allow, such as people in your Favorite list, or someone who calls twice in 3 minutes, etc... You can also enable Do Not Disturb for set hours - say 10PM to 9AM.