AT&T CL83451 Cordless Phone not retaining Caller Log

I assume you mean doesn't retain the CID information. Manual found here. Are these calls that were answered or did they show as missed calls?

Neither, there is ONLY a timestamp (all of them with a timestamp ending in 6 (xx.x6). I wonder if there a coralation with the handset lighting up for a few seconds. As I worte, my hard-wired phone does show the caller log correctly.

As near as I can tell the CID settings are correct. I also unpluged and removed Batteries from everythinng, to see if that it needed to be reset.

All the information comes from the base unit. If you also reset the base then there's a good chance the base unit is bad.

Sounds like a bunch of (Edited per community guidelines) to me. Voicemail and your phones answering system are totally separate services and one doesn't affect the other. I don't doubt Frontier may be sending out a nonstandard FSK code that maybe VTech and AT&T phones don't recognize. Think about how many of those phones are out there and all the different providers they are on.&n(Edited per community guidelines)p;

BOT got me for B-S

Here's what I'm betting, based on experience. The FSK code that notifies you that you have a voicemail message (yes it's also an FSK code) is of such nature that that it's close to the CID FSK code but can't be deciphered by the VTech and AT&T phones (which are made by VTech), so it gives you garbage. If turning off your voicemail, which turns off the notifications, fixes it, that pretty much proves Frontiers FSK code(s) aren't pure. This is a Frontier signaling issue not the phone manufactures issue. FSK is simply a method of sending data over the phone lines, different codes carry different data. 

Sorry did not see your post before I wrote this

Let me respond without using expletives.... Verizon sold its properties to Frontier. Frontier has not done a great job of supporting landlines (and why should they, it is a dying product with only 34% still having them) To say that my "Voicemail and phones answering system are separate services and one doesn't affect the other" may not be correct. The services may be separate, but that does not mean the coding behind those services is. Frontier has dumped Verizon's coding and replaced it with their own and I will bet they bought it from a third-party vendor. We (you and I (Me with over 35 years of Telecom Network Design experience)) have no way of knowing the quirks that have been created from a Verizon/Frointer Frankenstein system.  As for how many phones would have the problem, there must be quite a few since Frontier put out a service bulletin on how to correct the problem. The bottom line is that their fix has worked and I am no longer receiving ghost calls.

Their fix is to not use the FSK code that's bad out of their message waiting code for their voicemail. You'll have to tell me the correlation between an answering machine and voicemail. Other than setting which answers first which the user determines.