I use it with Vonage VoIP. I linked it to our two I-Phones, imported the address books from each. I programmed the Vonage voice mail, it even lets me know when we have a Vonage voice mail waiting with a flashing LED on each handset! A snap. Seems to be good clarity, can answer/dial through the bluetooth link to each cell phone. Works great when you forget to turn the ringer back on your cell when you come home, the Link-To-Cell rings for you.. and pushes your I-Phones customized ring tone through the handset so you know who is calling. It also announces the caller ID if you choose.