Great news- there is a resolution. I had called Vtech in December regarding the same issue. Just as stated above, I was told that it was an iOS10 issue and an update was in process. I called today and they have model DS-6722-3 which is compatible with iOS 10 and will ship it to me for free! When the operator asked where and when I purchased the phone, I was honest and told her I purchased it on Amazon, from a third-party reseller. There was no hesitation. She documented that and initiated the return process.
here is what to do. Call the Assistance line from the website:
1-800-595-9511
Mon – Fri, 6:00 AM – 6:00 PM Pacific Time.
Once you get through all the If-then questions and finally get to an operator, let them know the problem. They will create a UPS return label which will be sent to your email. Once I package the phone and the computer registers that my phone has been shipped, then Vtech will send me the updated model.
It was very easy. I am very satisfied with the resolution.