Those ones, mentioned in the previous posts, require a separate cell phone account and cell phone number. If you'd like to have something that works with your existing cell phone, you can use a Cobra PhoneLynx:
**broken link removed**
You can get them from Walmart or Amazon. I use one of these because I also ditched my landline a couple of years ago, but like the convenience of using a standard landline phone. The PhoneLynx makes the old landline phone work almost exactly like it used to. You can dial out calls from the landline phone, the caller ID works on the landline phone, etc., incoming calls will ring the landline phone. Since it works over bluetooth, you need to keep your cell phone within a reasonable distance of the PhoneLynx. Mine works as long as my cell phone is within about 40 feet of the PhoneLynx. It's also a good idea to limit the length of connecting cord between the PhoneLynx and the landline phone, because I found that with more than about 20 ft. of phone cord, the caller ID info becomes erratic (but the audio quality is still just fine).
Edit: Sorry, I misread your original post. I missed the part where you said the Panasonic can pair with a cell phone. In that case, it will most likely work without any additional hardware, but you will have the bluetooth distance limitation. If the panasonic phones are cordless types, then you're probably okay as long as the cell phone is located near the base unit.