Calls between my new iPhone 15 and certain Samsung Galaxies are introducing a lisp sound

I am updating this post with developments after my last post (on November 13), just to round out the record for anyone else who may experience a similar issue.

• Just after making the original post above, I requested an Apple iOS update/bug fix. In that request, I linked to this post. I never heard back from Apple.
• My mom borrowed a ton of other people’s phones in WI to make more test calls to me. Virtually all of them made it sound like she had a lisp, so the problem was definitely not her phone.
• My mom went to a Verizon store in WI. The store manager refused to look at her phone, saying “I guarantee it’s not the phones.” Rather, he suggested that our family switch to AT+T or another carrier. A surprising sentiment from a Verizon store manager!
• Meanwhile, I had spoken to yet another Verizon representative by phone and was instructed to visit a Verizon store for more help. From the Verizon website, I saw that there were both “company stores” and “authorized retail outlets.” I chose “company stores” in the hopes of getting the best service. The Verizon online appointment scheduler asked me about the purpose of my visit, and I was able to select “troubleshooting” from the menu . . . leading me to believe that I would be able to get troubleshooting service during the appointment.
• I went to the Verizon store for my appointment as scheduled. I was ignored until nearly two thirds of the way through the scheduled time slot, whereupon I was told that the store does not provide troubleshooting after all. The Verizon store manager told me I needed to talk to “tier 2” technical support by phone, which seems like something I could have done from home. This store was a nightmare in other ways, which I have reported to Verizon, not that they care.
• Verizon’s “tier 2” support person tried a bunch of things as had been tried many times before, including reprovisioning the phone and resetting various settings. None of this worked. Finally, he connected me to his supervisor. She said she understood that “this is a network issue.” She said that she would put in a ticket so that “network management” could check the network between CO and WI, and that she would call me back at a scheduled time.
• I reached out to Apple via chat to inquire about getting an extension to the standard 14-day deadline to return the replacement iPhone (new iPhone #2) if it wasn’t working out for me. The person on the chat said he could not do anything for me, but would connect me to his “seniors,” who could help.
• Someone from Apple called me as arranged by the chat guy. This person said that he was in tech support, not sales/warranties/returns, so he could not help me. (Thanks, chat guy!) However, given his experience working at Apple, he thought that Apple would not take the phone back from me, because I no longer had the one with the original serial number (new phone #1, the one that the Apple store kept when they gave me a replacement phone). “They will only take back an item with the original serial number on it.” I asked what my recourse was if the replacement product itself had a defect. He said that if Apple looked at it and now Verizon was working on the issue as the carrier, it doesn’t have a defect. I responded that I didn’t know that to be the case; I was just asking for more time so Verizon could finish looking into it, but at the end of the day, if they could not fix it, this arrangement wouldn’t work for me, and I would want out. His response to this was: “ultimately, the burden is on the end user to identify the root cause of the problem.” That’s an exact quote. Isn’t the burden on you, Apple tech support, to identify the root cause of the problem? I would have thought I did my part by paying over $800 for a phone, and by jumping through every hoop imaginable on the part of both Apple and Verizon. Also, I am certain I was not asked for my STEM credentials when I bought the phone, but I guess I am not qualified as an end user?
• After Verizon once again blew through a scheduled appointment time without calling me as arranged (not sure I mentioned in my original post that this had already happened before), I filed an FCC complaint.
• The FCC complaint finally got Verizon’s attention. Someone from “Executive Relations” reached out to say that they would be looking into the issue.

• Verizon still had not solved the problem by the last day of Apple’s 14-day return deadline on phone #2. I went to the Apple store again and had them replace the phone again (so now I am on new phone #3). At Apple’s instructions, I set up the phone as a new phone, with nothing coming over from iCloud. Still, on calling my mom from the store, I could hear a lisp.
• I set up Google Fi on phone #3. My understanding is that Google Fi uses T-Mobile’s towers, so it’s totally separate from the Verizon network. My mom sounded noticeably better on Google Fi than she had before. (As a side note: Google Fi advertises a 7-day “free trial.” However, I canceled my account after less than two days, and they sent me a bill for $77.84, which after endless rounds of emails with their staff, is apparently not something they will budge on, so . . . avoid that company if possible!)
• I then ported my number over to AT+T. Again, my mom sounds noticeably better than before. Meanwhile, Verizon has closed the books on this situation with the conclusion that their network wasn’t at fault, even though the lisp was horrible on their network and not on others.
• The problem with where I am today is that even though the lisp is definitely not as bad on AT+T as it was on Verizon, and my mom no longer sounds like she has a chipped tooth, the call quality is still pretty bad. When she calls on sister A’s iPhone 8 plus right next to me in CO, she sounds crystal clear, just like herself. When she calls on my new iPhone 15 (replacement/version #3), now on the AT+T network, she still sounds . . . not good. There is still some audio streamlining happening, voice isolation or something, that makes it sound like she’s got something in her mouth. It’s still noticeable, and worse, on What’s App. My dad also sounds bad still, too.
• Conclusion: switching from Verizon to Google Fi and then to AT+T helped to a noticeable degree, but it didn’t totally eliminate the problem. The call quality is really not acceptable even after switching.
• Next steps: I really have no idea. I have reported this issue so many times and gotten nowhere. For the past month, it’s been nearly a full-time job for me (and I already have a real full-time job). The frustration and psychic hit points are mounting, as well. After all this work, do I need to buy a second, cheapo phone (non-Apple) and pay for a second phone line just to talk to my mom? Do I need to leave the Apple iPhone ecosystem altogether and just switch to a Samsung Galaxy or something—a process that I am sure will be full of new and untold hassle?

Hi Vojtys, I am sorry to say that this problem has not been fully solved. Switching cell carriers (from Verizon to AT+T) helped somewhat, but it did not completely fix the issue. My mom still sounds like she has a lisp when I talk to her. I have reported this issue to Apple several times, but they are not bothering to fix it.

There is literally nothing you suggest here that I have not already tried, as detailed in my original post.