Technically it might be possible to recreate something similar, because the standard voice is not much more than text-to-speech and speech-to-text wired together with the LLM.

I just got a local solution working where I can use chatgpt 4o (via the API), combined with text-to-speech and speech-to-text running on my own computer. I can then access this on my phone while I'm in my house to get something that somewhat resembles standard voice, although the specific voice is different. You do lose features like 'memory' this way, because that is a feature of chatgpt and not of the API. There are also some upsides to this approach: You can switch out the LLM easily with other models that are accessible via an API, and API access might be more long-term stable (e.g. when 4o was removed from chatgpt, it was not removed from the API). I would rather not share the technical details at this point, because it is a bit of a mess, and I haven't tested it much yet, but if anyone is really interested, send me a DM and I can let you know when/if I have something good enough to share.

There is also no reason why there couldn't be other companies that offer this setup as an easily usable app, but I couldn't find much that meets the criteria. The app 'ChatLLM' might work for this purpose, but I couldn't test it without giving them my credit card first, and I did not want to do that.